Never give in to a tantrum. Let themselves wear themselves out if need be, but never give in. I have known of parents that leave a store, grocery cart full, in order to not give in to a child giving a trantrum. Its not fair to the other shoppers to have to hear it, for one, but above all, never give into tantrums.
What is more appalling now, is that more adults than ever are throwing tantrums to get their way, which a whole other problem in our societies. Same rule applies however....NEVER give in to a tantrum, no matter what it is "dressed up" like.
Peacefully, ignore tantrum throwers, unless they are hurting others, and then its ok to seek further help I think. Its all a big test.