I would argue it's not the sex that is specifically the problem, sex is clumsy for everyone in first experiences. For the incels it's the part before the sex they are erring on. We don't have socialisation classes on what typically occurs before the sex, we only have movies for that and the movies are not actually a reflection of our current reality. They get taught the wrong thing, fail, build up insecurity about it, fail even harder, and then resent society for it. This resentment at society for this makes them uniquely susceptible to the deep hate that the community has now become a hotbed for, including the mass killings carried out by some of them.

If I wanted to turn this around I think my starting point would be movies. Specifically movies focused on inceldom and reforming from it but also followed by a change in the way movies currently teach people these relations in an out of date way that simply isn't reflecting current society.