I remember a guy I was seeing. Well, not really seeing. We would run into each other at the home of a mutual friend often, and I had a huge crush on him, and we would fuck like crazy. The first time we had sex (which was within about ten minutes of meeting each other, and the sex was mind-blowing) he told me that from the age of 5 or 6, his father used to fuck him. This guy is Latino, by the way, and to him it seemed to be a cultural norm. He was also extremely pretty, and I just adored him. When he told me his father had been screwing him since that age, my reaction was one of shock. I don't know if I said anything, as I usually just keep my mouth shut while trying to be supportive. I was really stunned when he told me he really loved it, and his father and he stayed lovers for most of his life up to that point. He was at that time in his early-to-mid-30's, I believe. I must say that while I'm pretty open, and generally let folks do whatever pleases them, I felt there was something inherently wrong here, although he seemed to be perfectly well-adjusted and a nice, normal young Gay man.
In my own life, I was getting hit on by older "chicken hawks" from the time I was 16, and one of the first ones ever actually paid me to have sex with him, and he was very sweet, gentle, and it was I must say, very hot. Once, however, when I was 14, another guy, a classmate who was much bigger than me, brutally raped me and beat me up, and I had a tough time with guilt for years, although I got to see him get his come uppance when another classmate, who was on the football team, witnessed this guy trying to beat me up shortly after that incident, and just pulverized him right then and there. I also got my own revenge by calling the guy's father and telling him what his son had done.
Another time, when I was about 22, a guy I met on the beach in Hawaii and I hooked up, went back to my hotel room. The sex started orally, and was fine until I got on all-fours to let him fuck me. Instead of being gentle, though, he began to just slam into me, causing me to tear open and start bleeding, and when I tried to get him to slow down, he pinned me down on my belly and brutally raped me. He had ten inches, so this was very dangerous and extremely painful. I had a bad time with guilt over that for years. I might like fantasy rape, and group bath house scenes, but that's just play-acting, fantasy. The guys don't usually do that for real, and now that I've developed some abilities at self-defense, I'm better able to take care of myself.
I guess if a guy were to tell me he'd been harmed in that way, I'd simply stay close without crowding him, and let him know he has my support.