The lower classes i.e. the underclass, lower, working, & lower middle class hate the rich because they WANT to have that lifestyle. They see the rich having opportunities that they clearly don't. They see that the rich have influence & respect in society that they don't have. The rich have power while they don't have power. They feel as if they are personae non gratae by society.
The lower classes also contend that while they are suffering, struggling, & trying to keep their heads above socioeconomic waters, the rich have it made in the socioeconomic shade. They hate the rich because the latter don't have to struggle as they do. The rich, in the eyes of the lower classes, never have to worry about increasing costs of living, medicine, & housing while they are constantly looking over their shoulders to ascertain if they will survive another day. They must worry if their bills are going to get paid while the rich can pay their bills.
There are others of myriad socioeconomic classes who strongly avow that there shouldn't be any rich people when there are poor people. They contend that the rich got that way because of some corruption on their part, no realizing that the rich worked smart & made sacrifices to get where they are. Such people want equal distribution of income across the board. They feel that there should be a maximum income cap in order to prevent extreme inequality in incomes.
These people feel that the rich have excess income which is better being distributed so there are no poor nor impoverished people. They see it as a great injustice that some people can live luxuriously while there are others who constantly struggle & eke out an existence. They want everyone to have a semblance of a middle class lifestyle, with no extremes of poverty nor wealth.