Never. Quite possibly, this is the cruelest thing that you could do to someone. Particularly when you don't understand it or only know part of the truth (at best), anyway. Let people live; let people learn.
You let go of toxic and unhealthy relationships not because you no longer love those people but because you are strong enough to understand that there are times when people will be a lot happier if they go their separate ways than if they stay together..