There were some "trained Marxists" in my dorm in college, who spent hours at a time discussing the fine points of Marxist theory. They were all white and very rich, and made fun of the real working-class and people of color in my dorm. I've also known and worked with genuine, card-carrying Communist Party members (some in my family). They were all dedicated and idealistic people who placed the welfare of others over that of themselves. That proves your point that we should engage in "critical thinking" instead of knee-jerk reactions to labels.