It seems like you are reading something into what people write that isn’t their intention. No one is arguing that we should support local bike shops with bad customer service. We want to keep the good local bike shops alive! Even at good large shops, it is possible to have bad experiences — if you get a relatively clueless sales associate instead of the guy who was a former semiprofessional racer.
Once you fall outside of the pattern of the average customer, though, this requires more and more specialized knowledge. “My” local bike shop does bike fits, but it does have its limits. For an in-depth bike fit I have to go to another shop, where they offer several different types of bike fits, starting from a simple one to one where they use lasers, motion capture and all that. But that costs. And to the cost conscious crowd that is the average consumer, spending $300 on a bike fit alone is not something they’d even seriously consider.