I'd say that greed may be the most powerful emotion. Greed can prompt us to do things that harm others (like robberies, possibly murders). And all in all, greed prompts us to ignore others to get what you want, which may include ignoring homeless people.
Love and hate are the most powerful emotions and more often than not the two are intertwined. It's very likely that Hitler loved his mother who died when she was being treated by a Jewish doctor, the love turned into hate for the Jewish religion and culture and the rest is history.
Pride is also extremely powerful although I'm not entirely sure if I would define it as an emotion.
i'd say Jealousy, Love and Hate. Jealousy can lead to just about anything, Love binds people ( or people to objects/animals) and can cause very illogical thinking; Hate is also irrational and can be very consuming if left unchecked.