In the end his friends are irrelevant to the bigger picture. He makes it clear that becoming an agent of evil is the worse scenario.
Only if Yoda is certain about Luke’s turn and his inability to help. But why say “if you honor what they fight for” they should die, I don’t get that part. You can’t help people if you honor what they fight for? To make it clear, of course I do understand that Luke is not ready to confront Vader, but the way Yoda explains it to Luke doesn’t make sense to me.