You seriously think that other sources are free of errors? Newspapers for example??
At least with Wikipedia when errors are found they can be removed.
Also, in any GA/FA quality article there's lots of references; you can actually go to those sources and check stuff.
Just because there's a lot of non GA/FA quality articles in there doesn't make Wikipedia useless, it just means it's still being written.
I mean, Encyclopedia Britannica has been going for more than one century; Wikipedia is only just over a decade old, and is literally a hundred times bigger it covers much, much more; but it's about as reliable as EB.