What could have possibly compelled you to make this thread?
I don't believe he is actually suggesting that abortion policy should be driven by political demography. This is a forum on political demography so wondering what the effects of policy on it is an okay thing to wonder about (though as I indicated, any effects in this case are questionable).
Would it be wrong to ask whether policy toward immigration reform would be a demographic plus or minus for a certain party?
This might sound weird, but I actually thought his question was actually a pretty interesting scenario to ponder. Then again, I read it as "suppose the government (doesn't say which party) managed to get pro-life legislation passed that reduced the number of (legal) abortions, would Democrats actually benefit more than Republicans due to demographic advantages."
Rereading the OP, I can certainly understand how someone could misread what he said.
I might comment more at length, later about the possible effects.