I think anger at people who are deliberately oppressive, and an oppressive system, is justified and can be healthy, both as an agent of change and a step toward accepting the things beyond your immediate ability to change (you know, steps of grieving and all that - it's one of the steps to acceptance). I think frustration at people who are unwittingly perpetuating oppression is equally understandable, though it can be helpful to remember that often people don't know any better, and if they did they might well change.
But I think hatred is not necessarily a productive thing or a healthy thing, especially when directed at the accidental oppressor, or even entirely innocent member of an advantaged class, rather than the deliberate oppressor.
From the perspective of caring for yourself and your own emotional state, I've found hate to be a draining feeling, something that makes you feel worse over time as it mounts and perpetuates itself.
From the perspective of engendering change, it can be unproductive because it can lead you not to want a dialogue, to ultimately crave separatism, where the oppressed class can just live entirely away from the oppressive culture but also all the people who were advantaged by the oppressive culture. As a person who would prefer to dismantle oppressive systems and mindsets, hating all people advantaged by those systems and mindsets doesn't bring me any closer to that goal. It probably would make it harder to work with allies from advantaged classes and forge friendships with them. It would also make it harder to see members of the advantaged classes as potential allies or even potentially good people, which is defeatist in that it leads to an attitude of, "Why try, they're all awful anyway", and also problematic in that it's a form of unfair stereotyping, classifying advantaged people as inherently more bad or more worthy of hatred than disadvantaged people.
I'm hardly saintly enough to advocate loving a deliberate oppressor, and am pretty ok with hating someone who deliberately harms others, but it doesn't seem fair to hate anyone who hasn't earned that hatred by their own actions.