> lol its not a diversionary tactic
Yes, it is, along with being a fabrication and an implicit ad hominem.
> plenty of people get the back door banged for years and years and years with no problem, some decades..
1. As pointed in the the text covering logically-fallacious diversionary tactics: The burden of proof rests on the claimant.
2. That is highly improbable due to the fragility of the regions involved not to mention widespread (willful) ignorance, misinformation, and disinformation about anorectal anatomy, physiology, and health.
In the past I wrote material along these lines: "At best, anal intercourse and significant anoreceptive activities accelerate or guarantee the development of anorectal health problems. However, that could in theory be untrue if such activities are done with ridiculously excessive care all the time, every time."
"Ridiculously excessive care" was defined as adherence to precautions including—but not limited to—these: ruling out preexisting anorectal conditions (possibly caused by prior erotic 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 something is wrong — anally [below the dentate line], but not rectally [above the dentate line]), etc.
I then pointed out that 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, pornography sets a very bad example from which some (probably far too many) viewers get ideas, and people with (self-)destructive tendencies are having a field day.
> never thrusting too rapidly ("too rapid" could vary for different people, at least for the anal tissues)
"At least for the anal tissues:" The perianal skin and anoderm are capable of thickening, becoming tougher. I have seen no evidence that the simple columnar lining above the dentate line has that capability. Furthermore, it lacks somatic innervation, meaning that damage to it elicits no pain sensations (so good luck figuring out what constitutes "too rapid" there; the internal hemorrhoidal cushions also lack somatic innervation).