I agree with a lot of what you wrote. It's true that there is a "keep it for the elite" mindset in the back of many programmers' mind. For years at forums I've seen that while I tried hard to explain basic concepts to newbies, others were happier with the RTFM answer.
Still I'm not so sure that UNIX (or programmers) is the source of it. I started with DOS (later Windows) and TP (later Delphi) so please don't think I'm biased here.
I have recently bought an Acer convertible for my mother with Windows 10 and so I'm getting a reality check on the sad state of computer usability in 2017. Teaching her to use an Android phone was difficult, but this is not better.
IMHO the reason of user-hostility is not some guild mindset, it's just that computer adoption is needed much faster than the time it would take to develop decent GUIs. The RTFM knee-jerk reaction comes later from people with some deep insecurities and not much imagination.
Totally agree on that UNIX is also a sort of walled garden. I'd say the same thing about GPL'd ecosystem, in this case for license issues.