I'm not entirely sure it's become mainstream and I'm not entirely sure this is as dangerous as you suggest. Despite the obvious negative connotations, I presume that Black students also participated in this and presumably not against their will. If that were the case, then we can presume they had the autonomy to stop such a thing but chose not to - and perhaps the entire thing was an exercise in irony? The reality is, I don't know. What I think we should probably do is speak to the Black students and ask them how they feel. If white students were simply co-opting Black students in and pretending to sell them without their knowledge or consent then this is hugely problematic and needs to be addressed - but I also don't think it indicates 'white people are obsessed with re-enacting slave auctions'.

Here's a parallel. I'm against marriage and weddings in particular, because I think dressing women in white, requesting they be 'given away' by their fathers, that they pledge themselves to another man and take his name is endorsing the single most oppressive institution women have had to contend with for the entirety of human history. Marriage has been a form of control, is still used that way in some places in the world, and even is a thin veil for paedophilic practice in some cultures. I think, even if you strip away the horrible bits and keep the nice bits, it's still pretty reprehensible and I've held this view since I was 15. But if another woman in my life wants to get married, I show up, I eat cake and I dance my little socks off. It is their life and it is their choice.

In this instance, these students (for whatever reason) have seemed to go along with an ill-thought through event of their own volition. They perhaps feel differently to you - and we cannot assume they are ignorant of the facts simply because they don't subscribe to your view of what constitutes how to resolve the issue of racism. I'd say the same about beauty pageants and feminism - it seems problematic, but you have to speak more closely to the people who engage in them to find out what's happening here.