I do think that a line is being cross when they start shaming and judging people for being white or expecting white people to feel guilty for the body they were born in.
What line would that be that had been crossed?
Provided something like that had ever happened, and I've seen complaints about it exclusively by White supremacists: Why would someone, say, black work to make Whites feel shame over their skin color? Any idea? What could be the desired result of such action?
There once was a psychological test, subjecting Whites to the - non-violent - treatment routinely meted out to Blacks. That didn't go well, for more than just a few of those subjected to that treatment before long started to fight. That was just minutes of a treatment Blacks routinely experience for much of their lives. None, I wager, previously thought much about that kind of treatment.
So, I'd say, helping folks taking the perspective of the Other can lead to quite a bit of learning. One way to help them might be to give them a small dose of what Others receive for a physical attribute given to them at birth, and that's also the line being crossed: After all, that treatment was never meant to be meted out to Whites, and in a systematically racist society it is untoward for the dominant group even to learn about what, really, they are doing to Those people, for that might involve learning, and learning is the first step towards change.