I always regarded that as one of the good reasons for ending prohibition. But with one concern about meth in particular - my roots are in a place where meth use is rampant, and I know more than my share of people who use the stuff (and BTW nobody who has successfully quit). During the time when they are still healthy enough, they tend to go at it like rabbits, and the meth doesn't seem to impair fertility.
We fostered three offspring from such a couple. Took them in at high school age so we didn't have total impact, but of the three the oldest is headed for big things, one of the younger twins is leading a drug free (if not otherwise hugely successful - she has hooked up with a real loser) life, and the other twin is in on track to end up just like her mother. We're still working on her, she's not beyond redemption yet. Obviously, drugs being illegal is no deterrent to her. What needs to be continuously pounded in is that they will ruin her physical and mental health. She ought to know, looking at her mother the textbook example of a long term meth user, but just as her mother rationalized her own special way of doing it as being not harmful, so does the girl. She has at least cut down, as evidenced by increased appetite and weight gain, but she has been through a couple of those cycles.
Two are not doing drugs, one is.
With a two to one ratio, the pool is being cleansed.
If the parents die then the offspring are able to be brought up in a household that doesn't have the actions of drug abuse to copy.
The pool gets cleansed, one way or another.