Sterilisation of drug addicts
Now, you could reasonably argue that society would be a better place if drug addicts do not breed. It is likely that their children will not have a good start in life. You could probably come up with counter-arguments to that as well, although the point of this blog is not to get into that argument.
Rather, what concerns me is the ethics of the vasectomy under those circumstances. Before a doctor carries out a medical procedure, the doctor must ensure that the patient has given consent to the procedure. That consent must be fully informed and freely given. Guidance from the General Medical Council, quite rightly, points out that any consent a patient gives to treatment must be voluntary and not the result of pressure from other people.
The primary duty of a doctor is to care for the individual patient. It is not to act on what might be best for society at large. Whether or not it would be better in a wider sense for society if drug addicts are vasectomised is not the point. It strikes me as highly unethical to vasectomise someone who is agreeing to the procedure simply because they have been bribed to do so.