Here's an example of how I tried to explain: "Racist" does not mean "hateful" -- it means having power over people of other races and believing in stereotypes (prejudice). As a person with white privilege, I was given power and taught prejudice. Unlearning prejudice and working against my unfairly-given power is a lifelong task. Privilege is not a choice. There are different kinds of privilege, sure, and you can have white privilege without having male, non-disabled, heterosexual, cisgender, neurotypical (etc) privilege, but that doesn't change the fact that the system gives you privilege whether you want it or not. Privilege is automatically connected with passing as white, regardless of what you want or how you identify; you're going to get more of the good stuff and less of the bad.
I think most of these people have the capacity to understand, but their narcissism is blocking it. They're more concerned with looking in the mirror and seeing someone "good" (which means, among other things, "not racist") than they are with actually BEING good -- which means, among other things, actually working on their racism. I've seen again and again, people show amazing compassion in some cases, yet when confronted with the fact that their actions were hurting people, be so resistant to seeing themselves as "bad" that they caused more harm and showed no compassion at all. The compassionate response would be to say "these people are being hurt and it hurts no one to create a new theme, so let's do that." It's not the effort that stopped people; it's their unwillingness to see themselves as racist and/or products of society.
* if you don't understand why, here are some resources:
Open Letter to the PocaHotties and Indian Warriors this Halloween ::: Of Warrior Chiefs and Indian Princesses: The Psychological Consequences of American Indian Mascots ::: "my culture is not a trend" tumblr ::: a short intro to the understanding of white privilege ::: "Playing Indian" by Professor Philip J. Deloria ::: "Myths America Lives By" by Richard T. Hughes ::: "Racism Without Racists" by Eduardo Bonilla-Silva