I feel like the majority of people would still feel more positive about sex than negative. Otherwise our species would be extinct already. I reckon the minority having issues with it, to the point of having been brutally raped at some point, might not be enough to create a truly deadly devil. Also, a fear of STDs might not directly contribute to Sex Devil's strength. It's not the act of sex folks are afraid of but specifically the partner being diseased. Impotence or having been raped before would, in my opinion, contribute more to Sex Devil's strength directly, although I guess there could be Devil of Impotence separately as well. No man would want to face it, but fortunately there are female devil hunters, probably less affected by it.