No, the issue is not that extending human lifespans is ethically wrong (it may or may not be, but that's an opinion about research.) It's claiming that people working on such research are unethical people.
A very basic part about good-faith discussions is to discuss the topic at hand and not the people having the discussion.
Huh, I don't see the difference really here. If extending human lifespans is wrong (I think you and I agree that's not the point we want to argue), then doesn't that mean working to extend human lifespans is ethically wrong?
I think the conclusion of your line of argument is that you can never say a particular person is unethical. I don't think I like that consequence - it absolves anyone of guilt for anything.
In an extreme case, how about this: "Stealing thing is wrong. Therefore, thieves are unethical people." Seems clearly reasonable to me.
A very basic part about good-faith discussions is to discuss the topic at hand and not the people having the discussion.