DEI has become a bit of a four-letter word.
Making sure that people aren't discriminated against, overlooked for promotions, not hired, etc. on the basis of immutable characteristics like race, gender, sex, etc. isn't bad, and needs to be encouraged.
But the general feel of what DEI is is that it's supposed to encourage/promote people that belong to minority groups, and that can come at the expense of someone from a majority group.
If you're considering factors such as race, gender, sex, etc. when hiring or promoting, you're already engaging in some sort of discrimination. Now, some people do have bias, and sometimes (not always) that bias may be unconscious. But I don't think the answer to is to focus so hard on minority groups that you give the perception that you're discriminating against majority groups.
We've unfortunately let the extremes from both sides set the tone (far-left and DEI, far-right and discriminating against minorities). I say this as someone on the left, but I do blame a bit of this on the left listening to the far-left; Equal Employment Opportunities should be enough, but it wasn't for them; it had to go further.
And because of that, you're now seeing this backlash, and I have concerns on where exactly this will lead.
To further complicate it, things like "DEI" are defined and treated differently by different people; there doesn't really seem to be a standard on what it is. Are you just not discriminating or are you discriminating to help someone that has been part of a historically marginalized group? Because there's a difference.