a tailed beast becomes violent when things are out of balance.. it is a nature instinct left by the true purpose of the juubi.. balancing the world out.
the juubi wants to destroy humanity because in general, humans are not in balance.
kurama does not feel regret or remorse, because he is a beast of natural instinct.. not like a human being, he does not feel the need to avenge or corrupt.. he is merely a mirror of the person infront of him.. like a dog..