I think the larger issue is that usually when you are forcing yourself for a long time, your quality and quantity of work suffer. So I agree with you on the whole.

However the question usually isn't whether to do a task you don't want to but how to start a task you don't want to start out of fear or feeling like you don't have a grasp of it, or just aren't in the mood for it. If you can start a task, then you shouldn't have to force yourself to complete it. If you do, that's bad.

But there are things we have to do that we may not want to at any given moment. The question is how to structure one's work so they get done.