Tires appear to be a trigger for him. Guess you can't ask questions, anything other than what the factory recommends MUST NOT BE DISCUSSED.
Seems like a stupid thing for him to flip out over if you ask me, people posting on an MB car forum would most likely be airing up their tires however, factory, or 33, or 35, or whatever the tire says. IMO safe is a broad spectrum, not just a narrow line of EXACT adherence. If im gonna be worried about tires, im gonna worry about 100 PSI bald truck tires on trailers waiting to blow out my windows as I pass, and throw the truck out of control.
I say let it go, just ignore him or send a private email to a moderator asking their opinion and to edit the thread. In two posts he is accusing you of slander, anyone who reads it as an outsider can see its just a weird attack.
You start yelling back, then both of you become guilty.