I'm obsessed with the idea of being a serial impregnator, but I don't want to ruin anyone's life
What are you afraid of?
There's nothing to be afraid of. I don't want to hurt the girl and the babies too.
It sounds like you get some arousal or gratification from the possibility or risk of impregnation through unprotected vaginal sex.  There's nothing wrong with finding pleasure in the idea, as long as you don't separate fantasy from reality.  You should be okay with your thoughts and dreams.
Haha I'll stick to my fantasies then.
That sounds like the best idea.  Actually impregnating someone when they are not ready to have a child could seriously ruin their life, and yours too, since they could demand that you share custody or pay child support.