Not sure whether you're tone-deaf, but that 'course' sounds like it was remarkably poorly taught. The point is, racism is less (less, not exclusively one way or t'other) a matter of actions between individuals than it is SYSTEMATIC. That is, the system itself is SET UP to keep one group of people in the top slot. That is, people as pale-skinned as you and I. And that's why you made references to welfare as if most recipients are black or Latino (a majority of them are actually white). You didn't 'think' about such representations; the system presented you with them (without any explanation) and you accepted them without any conscious thought about them. Not saying you're a 'bad person'; this is what we all do UNLESS someone teaches us to ask questions and notice the 'glitches'. A question for you: when the teacher called all of you 'racist', did anyone ask 'How so?' Always ask questions; NEVER accept such real or ostensible blanket statements without asking short and to-the-point questions.