Fanon hole identified!
So. It occurs to me, thanks to lobelia321, that other than Goa'uld, I don't think we've actually had the angst-a-rama story in which brain-parasites-made-them-do-it.
Right? Right? If there is such a fic, you should leave a link in comments.
Seriously, guys, this is a significant hole in fanon, and we should all get right on filling it asap.