As for the point about not flying 3D when no one else is flying, how silly is that? Mid airs are very rare, I have not seen any with a plane doing 3D moves. In fact I don't think I've seen any with a 3D plane. In fact 3D flying can give other flyers more space. IF the 3D plane is being flown down low above the strip, then it leaves a huge amount of space free for other flying.
Try to remember back when you were trying to learn 3D, did you hover low??? probably not...were you in complete control all the time??? probably not...
Its o.k. to do it...just be respectful of others while you are doing it...