I mean, I'm sure there are adcoms who oppose it. My guess would be that they are rare enough that it ends up making little difference.
I would imagine there would be a larger percentage of adcoms who oppose the blanket URM advantage and try to take socioeconomic status into account when giving their nod of approval. My impression is that they're genuinely trying to create a fair playing field, and they're not just pandering to those who publish diversity stats.
My $0.02:
I really doubted the whole "advantage" thing coming out of high school. I went to a good public high school in a rural area, ended up doing well, and went to one of those prestigious private colleges. I probably had more "advantage" than 90% of the country, but at least half of this school came from that other 10%. I spent my first semester humbled and downright intimidated by everyone's accomplishments. I was among people who'd started companies and made apps and had been doing research since high school. They talked about SAT prep classes, unique twists they put in their college apps, and all of their friends at Ivy League/top schools. No one at my high school had ever even thought of these things as possibilities. Even immersed in that environment, it still took me 3 years to realize that I too could do things outside of what was encouraged back home (go to college/trade school, pull in a steady income, retire). Then I realized that if I (and I consider myself to have far more advantage than most people out there) took this long to adjust to the mindset, those who came from truly poor communities were at an enormous disadvantage.
We look around and see some kid sitting next to us, going to the same classes as us, eating the same food as us, and living in the same world as us now, but we completely forget that this person wasn't trained to seek out a plan and move to the next level the way we were. They're basically completely winging it, and if that person can succeed to the same or almost the same level as me, that person deserves my spot.