Because then we start training users to just ignore those warnings about self signed certs and effectively destroy SSL because man in the middle attacks are mad

Because then we start training users to just ignore those warnings about self signed certs and effectively destroy SSL because man in the middle attacks are made easy. and I just saw your clarification. Who doesn't use self signed for that? For that matter, you can do that within and organization and just push out your CA cert company wide. Save some money.