If a thing needs to happen, and the person who needs to make it happen isn't, and you don't think it's the nice thing to require them to correct their behavior, then you are misunderstanding the situation.

Necessity and nice aren't opposites.  Necessity means that the change has to happen - nice matters only in how you tell them.  Tell them nicely and politely what the problem is, and what your first thoughts on a solution are.

If they choose not to do what's needed, then you're not in a situation where nice applies, you're in a confrontation with a person who refuses to do what you require.