Let me play devils advocate here. The following is my NOT own personal opinion, but simply what could be used as a counter argument.
The sad truth is that some women have children to get money. This isn't confined just to addicts, but if they get money to look after the children who is to say they actually spend it on childcare? Even if they don't wish to do that, their addiction may overrule sense and logic and with cash in hand they will spend it on their next fix.
It is also a cheaper alternative to what Aribelle suggested. You may also provide these services but you have to rely on the addict to make the effort. Once sterilized, it's over and done with, one off payment and no chance of "no show". Yes this is putting it harshly, but remember this is just counter argument, not my opinion.
Another large aspect of addiction is prostitution, which can also lead to rape. Is it healthier for a woman for have 10 abortions, or be sterilized? Pregnancy takes it's toll on a woman's body from day one, and if she is weakened by her addiction she herself is at risk as well as the child. Therefore sterilization is for the benefit of the women herself as much as anything else.
My own personal feeling is much the same as the previous two. You can't dangle money in front of an addict and expect them to make a sound, logical, life-changing decision. Even if they have to speak to a counsellor a few times about it or attend meetings, as Aribelle said it is like resigning themselves to a life as an addict forever more.
Avatar & Sig by me.