I favor free sterilization for anyone who wants it. Where’s the downside to paying a little to have another Democrat spayed?
Oh, come on! Spaying is what you do to a pet! Who’d want a Democrat as a pet?
Well, I understand that you're just saying that in order to express the overall undesirability of Democrats.
But if your question were a real question, the real answer would be that sterilizing any human being --- Democrats included --- reinforces the norms that the corrupters of sex are promoting, that: sex is (or should be) inherently sterile; there is no rational argument against any kind of perversion; and natural sexuality is a social problem which can be solved by intentional impairment on a mass scale.
IOW, it just promotes their perverted "new normal."
And don't think that would limit their numbers. Like NAMBLA, they don't breed: they recruit.