Else we'd say abstinence is fairly reprehensible, since it also prevents the creation of new people.

Yeah, I realise they're quite related positions. I often feel guilty for not having had children yet.

Can we factor that in?

My guess is that because everything is linear, treating a fetus as being like 0.3-person-weight will give you the same answer as treating them as having 1-person-weight with probability 30%