I'm not positive, but I am pretty sure dictators use Communism to get power. It appeals to people in the lowest class, which is the majority it seems in the countries where communism took over. They tell the people about how everyone can be equal and the people with less like that.
I wouldn't say communism sucks, but it doesn't work. Also, I think saying communism is an extreme form of socialism is like saying socialism is a mix of communism and free-enterprise/democracy.