Marxism is dangerous is because it's utopian. Many of the worst crimes in history have been at the hands of people who genuinely believe they're trying to achieve paradise. Utopian ideals are dangerous because they excuse almost any behaviour if its aim is achieving this ideal. Surely it's permissible, even our duty, to eliminate anyone who stands in the way of paradise?
Egalitarianism is distinct from Marxism. Egalitarianism doesn't posit a totalitarian system to govern society and enforce equality.
I disagree. The wealthy and powerful aren't any more likely to be selfish and cruel than the poor. They only have a greater scope for acting on the flaws that are in every one our hearts. Any society or form of government is going to be flawed because humans are flawed. "Out of the crooked timber of humanity, no straight thing was ever made" [Kant]. We are not naturally angels. Greed, fear, violence, shame, status-seeking are part of our nature, as much as hope, compassion, reason, and altruism.
We are social animals. That means we care about other people. It also means we have strong innate desires to have status within our communities. Some people will always want to rise higher than others. In some cultures it's the number of eagle feathers in a head-dress. Or the number of cattle in the pasture. Or the number of wives, or the status one one's sons and daughters. In others it's the numbers of zeroes following the number in the bank account. Yes, ambitious people sometimes have unpleasant characteristics that go along with that characteristic (but then, so do the poor and apathetic). And yet, we all benefit from ambition. We're probably all be living in mud huts eating roots an grubs if it wasn't for ambition. Most of the great works of art we enjoy were created by someone with an unrelenting ambition for greatness.
I think the true flaw in humanity holding us back is the impulse to divide people into us and them that allows us to blame and dehumanize others. The wealthy. Foreigners. Muslims/Christians. Conservatives/liberals. We need to expand our radius of empathy to include everyone. That includes the rich and powerful.