this is an interesting topic!, so will add my two cents.
lol, personally I think this community works in my favor, as I've been into Yaoi for a few years now. If I come across a good story I like... all the better for me.
Personally I don't have to much issue with bad stories, if I think it's worth saying something or giving criticism I will, if not I just move on. It's how you learn and improve. Plus, my writing leaves a lot to be desired, but frankly I'd rather recieve a lot of criticism than have no comments at all.
If I'm looking for a particular theme or story, I asks for rec's, and usually I find what comes back is at least half decent. I'm not under the illusion that AFF authors and other communities with fanfiction will be of the standard of an officially published author. Even with a beta.
In the case of people with a second language, it may be better to be a little understanding. Sometimes there is a HUGE difference in the structure of languages that may contribute to an authors writing. If your picking up a dictionary for every second word in your story, it's a monumental task when you really think about it.
Of course, you get authors who are just outright bad, second language or not, haha.