For me it depends on the RPF. I was in Popslash, and I must say Justin Timberlake wound up impregnated several times to great effect.

With RPF, I'm much more ok with it when it comes from a case of crack or stage persona. MPREG Justin wasn't any weirder than Lance Bass: Llama.

But I don't get it about the actors themselves. It's not so much their public persona. And I'm of the opinion that -actual- children of celebrities should be left entirely out of it. You want a passing mention, 'oh, yes, I've a son, he lives with his mother', fine. But don't make them into characters.