Is finasteride, a hair-loss drug with fertility side effects, immoral to use?

Yes, I think you have a good case there, and it shows how careful we should be with any drug on the market. We live in a drug society where big pharma produces drugs for everything, and nobody lives with any condition anymore; there is a drug for it, and then you read the side effects, which can now include heart attack or death for the most innocuous problems, whereas before the 1980s they were not required to disclose them. Capitalism, for all its good aspects, has corrupted many virtues because everything is wrapped up in how much money can be made. So a drug like this, taken for something as minor as hair loss but risking fertility and birth defects, is a case where the moral calculus does not favor using it. Be very careful with these drugs, because many of them are doing real harm.