Private consensual acts include incest. They also include bestiality. I take it you're against a prohibition on both? (And don't try the bogus 'animals can't consent to sex' argument; they can't consent to being killed and eaten either, but we do that)
We pass many laws whose prosecution is made very difficult by the constitution or sheer practicality. Of all the instances when someone exceeeds the speed limit, how many are prosecuted? 0.01%? Do we argue against speed limits because to really enforce them we'd need massively intrusive action by law enforcement? Nope; we prosecute the speeders we catch, and hope that acts as a general deterrent.
Of course not. There are numerous acts that we all agree should be criminal, that can indeed be committed in private.
I don't think anyone is arguing that because something can be committed in private, we therefore must make it legal.
We pass many laws whose prosecution is made very difficult by the constitution or sheer practicality. Of all the instances when someone exceeeds the speed limit, how many are prosecuted? 0.01%? Do we argue against speed limits because to really enforce them we'd need massively intrusive action by law enforcement? Nope; we prosecute the speeders we catch, and hope that acts as a general deterrent.
This is reasonable.
But when it comes to homosexuality and adultery, I don't think the issue of legality is merely a pragmatic one when it comes to enforcement...but that the majority of Americans simply don't want people arrested and jailed for such things even if police happen upon such acts while in their house for some other reason.
And that is of course the circumstance of the case Santorum was commenting on.