Coal power definitely saved a lot of lives, and probably more than it killed, but it introduced new problems, not worse one, highly probably less-bad problems, but problems nevertheless, shouldn't mean that we ban coal tomorrow, but that we should (as we somewhat are) work toward fixing the new problems.
The same goes for all technologies, they generally save a lot of people from A but then causes B which is a new, less efficient source of death. This is one of the situations where we should strive to have our cake and eat it too. Hell, asbestos probably helped save more lives than it took, we just found something less terrible to replace it with.
It does not mean that its use was a mistake, but it's continued use would be, as we have an intrinsic responsibility to always seek safer alternatives when we discover the negative effects-