For emphasis:> Blatantly injurious erotic anorectal violence
As for anal sex or "butt sex" without qualifiers, here is an old post of mine that is very relevant:
(Quoting myself)> At best, anal sex and significant anal-insertive activities accelerate or guarantee the development of anorectal health problems.
That could in theory be untrue if such activities are done with ridiculously excessive care* all the time, every time.
* That includes, but is not limited to: ruling out preexisting anorectal conditions (possibly caused by prior sexual trauma), always using lubricant, avoiding lubricants that irritate/damage the rectal lining, avoiding enemas (all enemas, hyperosmolar or otherwise, probably remove the rectum's protective mucus barrier), always using a condom (particularly in the absence of an enema), never thrusting too rapidly ("too rapid" could vary for different people, at least for the anal tissues), never inserting anything too girthy ("too girthy" also could vary), never using numbing agents (pain indicates that something is wrong — anally, but not rectally), etc.
In practice using ridiculously excessive care is unrealistic — it'd be more of a chore than a pleasure. Furthermore, both ignorance and misinformation are rampant, porn sets a very bad example that some viewers get ideas from, and people with [self-]destructive tendencies are having a field day.