Unlike almost all other people I ride with, I find it easier and more economical to ride standing on almost any climb. I can climb standing for an hour without a real need to sit down. The only exceptions are technical trail climbs or very mild gradients where sitting is easier. I am aware this is a less economical position, but for me it seems to work. I can discipline myself to sit on longer rides but I find that my effort invariably increases. On my trainer I do complete all workouts almost entirely sitting down, rarely standing up (and doing it only when I need some relief).
I doubt it is an issue of bike fit as I have fitted my bikes and played with various positions. Another observation is that it is much easier for me to breath when not bent over the bike. But, mostly I think it is the form of my body (I have relatively long legs for my total height of 182 cm) and the relative strength of my muscles (I was more of a runner than a cyclist for many years).
Bottom line: Is it categorically wrong to spend a long time standing up, and should I really practice riding sitting?
Are there others like me out there who are constantly harassed 
about their wrong form?
No. Just ride the way it works for you.
And if anyone is giving you grief for standing on a climb, ask them to look up Alberto Contador.
Are the people harassing you faster or slower than you?
As above, I agree that doing whatever works for you is best. However, if the people giving you feedback are experienced riders and maybe see you burning yourself out on a longer ride, it’s atleast worth considering their feedback.
If you can climb standing for an hour then your body is almost certainly well suited for it. I get tired after 30 seconds to a minute. I’ve tried standing more often on climbs to see if it would make me faster. Mostly it doesn’t, unless I’m on a modest gradient like 5% average and in the big ring. Even then, I run out of steam after that half minute or so and the rest of the climb I’m slower than I would’ve been if I’d remained seated. On Saturday I kept an eye on my speed whilst on a fairly lengthy hill and I was invariably faster in the saddle. I think if you look at people who compete in hill climbing competitions, they almost always climb out of the saddle. It’s just more explosive but you need the power to weight ratio and the lungs to make it work. If you can, it’s chapeau to you, Sir.
I sometimes don’t have a choice. I just can’t muster enough power for some gradients in the saddle. OOS is my only hope when that happens.
Nothing wrong with it, if it suits you.
I am impressed anyone can climb out of the saddle for an hour. I struggle with more than a minute or two.
Only question I have, looking at styles in Le tour etc., if you climbed seated at a more constant pace/power, would you be quicker? Contador vs Froome/Demoulin.
Depending on the gradient of the climb (and rider’s position on the bike), sitting is probably going to be more aero for the same power… not to be underestimated on some long, shallower alpine climbs.
Whether one can get the same power out sitting is another question altogether.
Everybody is different, there’s no right or wrong.
It might be worth experimenting with though. Do the same climb a few times, seated and standing, then compare times, power, heart rate and perceived effort.
In my experience this can be highly dependent on available gearing and the adaptations that it forces on you. 10 years ago I was riding a bike with much more limited gearing, I adapted to doing most of my climbing out of the saddle and could eventually pace myself to stand for long durations. Now with compact cranks and 32+ sprockets on the back, it’s rare that I feel the need to get out of the saddle, and when I do it feels more tiring since I don’t do it very often.
Also be mindful of joint pain. Back when I did most of my climbing out of the saddle I also had a lot more trouble with my right knee. This has improved dramatically with wider gearing that has allowed me to stay seated and keep my cadence up.
Mike Woods has talked about this a bit. He says that being a former runner, standing feels like running, and he can do it for long periods of time. When he won that Zwift race, he had been standing for nearly an hour. You do you man.
Just make sure the seating police doesn’t catch you, and you’re fine!
I have no opinion about the sitting vs standing but I’m curious what your cadence is when you are 60 minutes into climbing while standing. Not that is matters. I just want to know.
I’m the opposite, I only get out of the saddle to sprint or to get started at a traffic light. Empirically, staying seated is more ergonomic, but IMHO you should do what works for you. If you feel better climbing out of the saddle and you can do this for an insane amount of time, good for you.
The only place where I’d say sit down is if you are mountain biking (you mentioned the word trail climbs in your post). Here, traction matters and if you sit down, you have much better traction. Also, when you are standing, you will have a more uneven pedal stroke, which means your force/torque will have spikes that may cause you to lose traction. So for mountain biking, I recommend you sit down for climbs. On very steep climbs, you must sit down and perhaps even bend over the bars to even have any traction on both ends.
Its all gearing dependent in my experience based on the grade.
Many thanks for all your input. It’s very useful to read your thoughts on this. I guess I knew there is no right or wrong, and that we should do what works best for us, but I am really interested whether preferring to stand is an acquired habit or derived from some aspect of my physiology.
@Wefty, I am typically at around 60-70 RPM when I climb.
@OreoCookie, I definitely do not stand when on climbs with poor traction and there are many of those. In those cases, I heavily lean to the front to keep traction on both tires, but I do stand as soon as the hard part is over…
@onemanpeloton, mostly slower 
. But of course, they all want to be helpful. Some wish they could do more standing, perhaps believing that would make them faster.
@PhilSJones, I think the answer really depends on the terrain and the gradient and the duration. There definitely are climbs that I do faster in the saddle, and some of my PRs on such segments are siting, but if I want to sustain power for a long time without blowing myself out I definitely stand.
This is really a great forum - another benefit of joining TR!
Sounds like a good summary: So if I have any advice (and I am cautious to give any), then it would be “EXPERIMENT”. See what works systematically, and work on strengths and weaknesses.
One other thought. I am a TTer, so I practice climbing hills and longer drags in the TT position. This is NOT because it is more efficient, but because I am practicing putting down a high consistent power over a period, (and climbing Out of the saddle on a TT bike, or on the other bars is less efficient). However when on my road bike, I deliberately climb out of the saddle for periods and often in a stupidly low gear, just for the training effect. Also I suspect (guess) you are quite light, compared with me. But that is just me…
I think the fact that you were a runner for many years is everything here.
Worked for this guy 
Side note: This was a classic stage in the TdF
Yeah, I think Armstrong mentioned that the other week when they did their Blue Train podcasts, may have been on the climb on the video above - said he stood a lot when climbing because of his triathlete background, felt like running…
Everyone’s hit the right advice on individuality.
I recall a study that standing is indeed less economical from a pure efficiency standpoint, so your mates aren’t wrong if we’re measuring energy depletion in the lab… but if we’re measuring what’s the fastest way for YOU to climb steeper grades then it’s gonna be the one where you can sustainably generate the most power.
I’m similar to you. My power is highest OOS. My HR is +5 BPM higher, but I feel far less perceived effort and the results speak for themselves. I generate the best power standing at 55~65rpm and likewise my friends make comments. Usually more shocked and surprised than anything.
I’m just built that way. Tried the sustained 90~110rpm thing but it hurts my power and speed. It’s better for bursty sprints not drawn out climbs.
I’d love to know if TrainerRoad has data correlating cadence/standing preferences to (trained) rider type. Maybe the majority once trained falls into the “spin to win” club so the outliers are left defending why they’re different with only their individual anecdotes. 
I’m not sure if this has any validity nor do I remember where I read it, but I did at one point come across something saying that lighter riders were able to climb out of the saddle with less of a psychological cost than heavier ones.
Seems to ring true for me compared to my group ride buddies, at least- I’m a fair bit smaller and spend a lot more time out of the saddle.