The explanation you were given is a pretty big oversimplification that ignores some very legitimate complaints that some people have. Of course there are those simple racists who don't even understand the philosophy behind DEI and are just generally opposed to any system like this, but there are also many instances of corporations, universities, and even governments taking it to the extreme, which results in kind of a "fighting racism with racism" situation. One example is Google being sued by an ex-employee over their policy to purge all applicants that were either Asian or white males. That's blatant racism in the literal definition of the word, and is illegal. Another example is California's failed Prop 16, which would have repealed the law that makes it illegal to discriminate based on race, sex, color, ethnicity, or national origin. The stated goal was that they wanted to discriminate against Caucasians and men for job applications and school admissions. Again, quite literally racism, and in this case sexism too.

While the situations like the ones I gave examples of are often made with the idea that they are helping, they're engaging in the very behavior they claim that they want to eliminate. Doctor Martin Luther King Junior famously said "Darkness cannot drive out darkness; only light can do that. Hate cannot drive out hate; only love can do that.", and likewise racism cannot drive out racism.

The crazy right wingers aren't the only people objecting to some of the implementations of DEI. Many Democrat and left-wing professors and activists have spoken out against what they feel is a misguided attempt to enforce complicated principles from DEI, but the detractors are often shouted down, ostracized, and accused of bigotry themselves. And that too has received condemnation from left-wing academics and activists, but their voices aren't loud, and they're not the majority.