I think being able to edit posts is generally good. There have been a few times I've really badly cocked up on a circuit or post, which would result in magic smoke if someone followed it and really needed to edit it. I could have posted a follow-up, but there's a risk it might go unnoticed. The majority of people edit their posts responsibly, so it shouldn't be ruined by the minority who are childish.
I've seen all sorts of really silly stuff during my time on the Internet. I remember when someone got banned from a forum, all the images in their posts were linked via image tags to their server, so they decided to change them to some dodgy porn. The administrator had to figure out a way to block their site from being used in image tags, which took awhile. Then there was the time when someone who got banned here, decided to come back and spam with forum with dick pics and child porn.