Because I am a woman in reproductive age who has just been pregnant, because I would like to again and because I realised when pregnant that I can't rely on someone else to be aware of their bodies and sometimes people might even ignore warning signs because they are horny and put me at risk!
I am taking control here by not sleeping with them...sucks for people with cold sores yes. I feel sorry for any person given it as a child by a selfish, ignorant or self centred person who didn't realise they shouldn't kiss someone with a weeping sore on their face but I won't put myself at risk and personally I enjoy kissing my children whenever I want to. I don't want to give them anything.
It is too big a risk for me.