To be honest there is alot of things actually bad, about sex between 2 guys.
1. The well i dunno medical term but your butt crack and in that area, contains alot of diseases and different things. So your basically sticking your member in to a pool of nasty stuff.
2. You can break a pivotol part in your colon with the force applied to that area.
I really wish i could remember where i found it, but im lookin it up and im doin searches, but having no results.
The place where i read it even said it in the way most people think
" Its an Exit, Not an Entrance"
That area was not designed for penetration..
So is it right, medically i say no.