If you want to be part of Wikipedia, anyone can and should go and start helping out.
Deletionism doesn't exactly encourage people from these groups to come help out. That, and the endless politics/bureaucracy have kept me from bothering to edit. Why make a change when it will likely be reverted?
A good place to start is to write an article on: 1) something you are not personally closely connected to; and 2) have information on, from decent third-party sources that you can cite.
Nobody I know who's done that has had a problem, though I obviously don't know thousands of people. People don't generally go around randomly deleting well-cited articles that don't appear to be self-promotion. I certainly write about all sorts of random stuff and don't really run into problems. But it's all stuff I have no connection to, and I go to the library to find sources for the articles.
The people I know who have had problems were mostly on Wikipedia to promote themselves, their project, or a project/thing they were closely connected to. A bunch of academics, for example, seem to think that a great place to start editing Wikipedia is to write an article about themselves, cited to their own webpage. Either that, or about one of their research projects, or a theorem they just proved, or a close colleague. All not very good places to start.
I personally find it hard to think of things that I'm an expert on, but have no connections to. I probably know more about the sources and articles about the university I attended better than I know or read about UC Davis for example. Also, since I have never been anywhere near UC Davis, I have little incentive to write on it.
Could I take random articles and potentially find things to cite for them? Sure, but would they really be the best citations? That I'm unsure of. I'm not close to them and I'm not really qualified to write on them or choose sources.
For example, if I wanted to write on Neuroanatomy, I could find plenty of citations, but they might be from shitty journals. But I don't know the difference between the good journals and the bad ones because I'm not in this field. It is entirely possible that I could write a very well cited article with plenty of citations that is complete bunk. Yet my girlfriend is working on her PhD in Neuroscience, so she would be much better qualified to write on it. Yet, she's perhaps too close to the subject?
How close is too close is a bit of a gray area, but a whole subject isn't really off-limits. I'm a computer scientist, for example, and write CS-related articles. But it's best practice for me not to write articles on algorithms or concepts I've personally invented, and ideally not those my advisor or other close associates have invented either. But something Knuth invented is fair game.
Deletionism doesn't exactly encourage people from these groups to come help out. That, and the endless politics/bureaucracy have kept me from bothering to edit. Why make a change when it will likely be reverted?