I've never flown a GA plane to Mexico so can't comment on that. But since I'm married to a Chilanga (gal from Mexico City) I airline there all the time and can make a few statements generally.
Indeed parts of Mexico are dangerous but then so is a lot of the USA. If you really want safe try Europe or parts of Asia. I won't travel near the border at all, too many druggies there for me as a gringo. But in the interior, the smaller cities and tourist or resort towns are fine.
As for bribes, I lived there over a year a long time ago and only paid a bribe once. It's no big deal but if that is absolutely against your principles best not to travel. If you do, generally everybody pretends it's a fine or fee or tax and you're on your way.
Basic Spanish or at least a few phrases are helpful. Like any place, if you show basic respect you'll almost always get it back. Traveling anywhere, even within the USA, shows that lots of stereotypes are bogus, and Mexicans have their own stereotypes and issues with us.
I do want to fly my RV there someday (like, uh, when it's flying here) and I plan on going the first time with somebody who's done it before. So I'd recommend that for sure.
As for the guy who won't travel back to Mexico, most immigrants, especially undocumented, are from the north where the drug gangs are worse. Or maybe the guy doesn't have legal papers and is rightfully uncertain he could not get back here.