And for all crimes they commit which violates someone's rights, they should be prosecuted. If meth or any other substance has a high probability of encouraging someone to perform violative acts, there's a strong deterrent from doing them in the first place.
Example: If I hold a knife in my hand, it is more likely that I will hurt someone than without it. This deterrent causes people to be more careful when holding knives.
Holding the knife itself is not a deterrent, just as using a substance is not in itself a deterrent, but the possibility of hurting someone else is greater.
