Socialism in principle sounds great, but most times it's been implemented it's suffered from the same problem as capitalism - the people with power are greedy and use their power to manipulate and oppress the populace.

This is true, the "dictatorship of the proletariat" is self-contradictory and impossible IMHO. Because as soon as a member of the proletariat is a dictator, they are now no longer a member of the proletariat.

Now you don't need a dictator, you can enact socialist policies democratically. This is very slow and kind of difficult, because the capitalists will lobby and fight so hard against it, and you need to maintain public support.