Not all drug addicts are equally bad. Some are able to suppress their habit on a temporary basis which enables them to be responsible in some ways. Examples include alcoholics are nonetheless able to get to work on time every day and hold down a job. People who “only” do drugs on the weekend, or after they get home for the day.
So yes, there are some so depraved as to pimp their kids… but not all of them are like that. Those that are able to act responsibly despite their addiction should be helped and encouraged - among other reasons, those are the folks with enough self-control to have a chance at driving their condition into remission long term. Which is something we would all like to see.