It is actually a very weak argument.
All you need to do is look at obvious intuitive laws.
Why have murder laws when there will always be murderers? Only law-abiding people will not murder?
I said I could argue pros and cons.
Yes, on one hand it is not the strongest argument for those reasons you give, esp in political fights like these.
He is saying that the new laws wont prevent murders and will only make criminals out of those who don't commit crimes with them now.
Suicide is illegal. How’s that working out?
IMO, laws against murder (for example) for the most part end up punishing the murderer after the fact rather than actually preventing murder.