Interestingly, you slip from the moral implications of this question to what might be called a "strategic" approach (as in 'how to deal with this phenomenon").

It is an argument with a certain amount of credibility.

But think on this: how willing would you to make the same argument for other moral problems?

For example, abortion. Precisely this style of argument was one of those advanced by pro-abortion campaigners (as in "if abortion is illegal, it won't stop. It will just happen underground ...).

For example, gun control. Again the argument would be 'better that people have guns legally than have them illegally".