UI isn't just a state a calm. It's like being in "the zone," as athletes call it. When everything just clicks, there isn't hesitation or a delay in thought and action. So you can be enraged and be in the zone, but you would have to have thought of guilt or holding back, no second guessing. Which is why the rage tap doesn't really work for Goku, because he is too kind hearted. It would make sense for Bardock because he grew up where casting everything aside for a battle was normal. Vegeta needs more chaotic energy because his overwhelming sense of pride and what he should be, overshadows what he is. So what he can do physically doesn't match up with where he wants to be.
