Universities which received funds, centuries ago, from participants in the slave trade are taking steps to educate the public about this.

I don't think that the universities are guilty for having received those funds, but educating the public about the slave trade and its influence is a good thing to do.

The point at which accepting donors from evildoers becomes a moral issue in itself is when they use you to buy public approval for their acts and undermine your responsibilities to the public. For instance, today, when planet roasters have positions on the boards of organizations that do science education, such as WGBH and the American Museum of Natural History, and when Bill Gates donates "Gates Buildings" for university computer science departments.