I suspect that historically it's not based on a sour-grapes mentality or inferiority complex, but instead on class issues. Historically, rich yacht owners and people who work in the marine trades were drawn from very different segments of society, and a kind of "if we let those grubby blue collar types onto our boats, next thing they'll be wanting to walk into the clubhouse through the members' entrance, and who wants that?" ethos may have been in play.
Actually, the historical record indicates that the class issue worked the other way around in many places. The rich of the 1800s, for example, were not fools. Many of them appreciated getting to know the "common people", and sailing allowed them to do that. I think it may be the letters between Herreshoffs where it was said that the Iselins, for example, were encouraged to sail sandbaggers because their father thought it was important for them to get to know the "commoners". The same was said around Sydney, where (despite persistent bullshit about the "skiffs" being the working class boat and the yachts being for the rich) both rich and working class raced skiff types together, and said that it was a good thing to mix the social classes.
In the 1890s, the UK's Yachting World featured a monthly section on a pro. There's nothing in those articles that implies that they are "grubby blue collar types". Many accounts of the time, like autobiography of pro skipper Diaper, show that the pros weren't particularly downtrodden.
While there was certainly a social divide, whether it was much bigger than that of today is another issue. I've sailed with some very arrogant owners who treated their crew no better than the typical paid hand of the Victorian era was treated, and reading something like Ben Ainslie's encounter with Hasso Plattner it seems that even he has received the same sort of treatment (or worse).
It's interesting that the excellent "Southern Breezes", a history of NZ sailing, says that the dinghy classes in very egalitarian New Zealand repeatedly fell apart in the early 1900s era because of the fact that pros won everything.
As someone who was effectively chucked out of a class I loved when they brought in "pro" restrictions, they seem to be reasonable. The typical sailor with a 9-5 job can't normally compete with a pro. Arguably, having no chance because you can't train as much is similar to having no chance because the other guy has a boat four times the cost and 25% lighter. We accept restrictions that reduce the financial cost required to be competitive and restrictions that reduce the time cost required to be competitive aren't vastly different.
The fact that the AC pros accept that time limits on practise are required for the good of the class is interesting. If they accept that limits on practice time in a class are reasonable, why can't "lesser" pros?