It's stupid to ambush them when he wanted Dante to be by his side. His plans were not like Mundus (though close), so offcourse telling them his plan he would think they would understand his point of view. He has a right to say that they don't understand after he said "not like Mundus" and that the world can't protection itself. It's just those words he put like "subjects", not thinking about Kat when they saved the humans only to put her as "useful",etc which cause worries for Dante. Vergil isn't evil to begin with (in fact, we didn't know what his full intentions were in DMC3, and he seemed like a good guy when we let Dante go in DMC1 in the first fight), and we have to wait for Vergil's Downfall to see if he'll be power hungry. But Really? The stupidest thing you've seen a videogame. REALLY?