I don't think there were ever white supremacists at the ACLU. Who would that have been? I think DEI is a heavy mistake to pursue. I get the incentive but the method is lacking and everyone will lose.
Sorry, the view is more that traditional civil liberties reinforces white supremacist power structures (I think the ACLU actually has a page on this?). So that those in the ACLU perusing what were some of those "traditional" civil liberties things (free speech etc) were supporting white supremacy. The ACLU has moved away from that towards some of the speech = violence approach which then basically allows a violent response.