All your examples aren't exactly valid.
- That's not "perfectly valid", it may be slightly broad since the answer depends upon the programming language. It may have been suitable for Programmers.SE, though (link stolen from @YahooAnswers).
- A beta is a beta is a beta. Members of betas know perfectly well that their site may be closed at any moment. If all betas are meant to be permanent, we wouldn't have a beta. The proactive steps are being taken by the community, and we are salvaging posts.
- Yes, this is sort of an issue-- I think there were sandboxen for these, but many are inactive. Remember that the SE engine is not open source, so visualization requires a whole new engine built from scratch. That's a whole lot of effort. In the meantime, use phpMyAdmin to trawl the dbs, I would say.
The general issue
It is extremely ironic that you mention Wikipedia. I used to volunteer there for a while (gonna start again), and they have this "hostility" issue much more than we do.
It's not hostility. Most people are just following the policy. Wikipedia has many more policies than we do, so the issue is more prominent there.
On SE sites, users do get scared off if they get reprimanded repeatedly (seen it happen).
Things like using patronizing tone when talking to newbies,
Well, I'm not too active on SO, but on smaller sites, this doesn't happen. On SO, I've seen some not-so-nice comments, but these usually apply to "do my work for me" questions. You can't really assume good faith here.
closing questions with very little or no explanation
The close reason is enough explanation. There is a closing blurb underneath it. If the actual reason for closing is slightly different from the CV reason, CVers should be explaining what to do to improve the question. But I'd need some examples about this.
and general snobbish attitude form senior members and moderators.
And note that we do usually AGF. Just not in obvious cases. Wikipedia does this as well.