As a libertarian, I generally oppose the state interference that is licensing. In most cases of professional (or occupational) licensing programs, I see no benefit that warrants state interference. ...
[However!]
3. The state should require parents to be licensed. That is, there is no moral right to raise a child, and we would do well to think of it as a privilege that the state grants and can refrain from granting to certain individuals. If you don’t like that way of putting it, I am comfortable with a weaker claim: whatever moral right to raise a child there might be is defeated when the parent-to-be is significantly likely to cause the child substantial and avoidable harm, or, of course, if the parent does cause the child such harm. Those that should be refused a license to parent a child are those who are likely, in parenting, to harm the child. Those that should have a parenting license revoked are those who do harm the child. (In our society, the latter is called "termination of parental rights" because there is an assumption of such rights. Its worth pointing out that I have not seen a good defense of the claim that natural biological parents should be assumed to have the right to raise the child they create.)
Andrew Cohen, at Bleeding Heart Libertarians
You know, Mrs. Buckman, you need a license to buy a dog, to drive a car - hell, you even need a license to catch a fish. But they'll let any butt-reaming asshole be a father.
Keanu Reeves, in Parenthood
Just saying, is all.
(H/t to Justin Green, who is slightly less terrible* for having put this on my radar.)
*He's still pretty terrible.