Not all the replies. I mean that some person on the post itself will remind the OP to get tested.

I won't deny that people automatically go to that if it's a mm relationship but I've seen tons of posts related to cheating on reddit with those suggestions. Go check out some posts on r/relationships or something and you'll see what I mean

Nah. Literally every cheating post that I've seen on reddit suggests this, most are straight relationships.