The female form is an ugly thing get it off yer wall!
Ok, seriously though, if you want to have dates over to your place, take them down. They make women uncomfortable.
Speaking for myself, if I was dating a girl, and then went over to her place for dinner and she had a poster on the wall of some muscleman with his dong hanging out, it would probably make me uncomfortable.
Your relatives want you to take the posters down because they are thinking that it will inhibit your ability to get a wife and crank out kids, and they are probably right.
On the other hand, if you are only gonna be doing the SP thing, and you don't want a girlfriend, leave em up!
Honestly, if I ever gave up on the dating scene, I would probably do the same thing. After all, I am still 14 at heart. What guy isn't?