I understand where you're coming from but it's really not that complicated.
Just answer these two simple questions.
1. Do URM's get accepted at a higher rate than white/asians at a certain lower threshold of GPA/MCAT?
AAMC statistics will tell you that yes, yes they do. Essentially, if getting into medical school was a simple accumulation of 100 points.. URM's are gifted an arbitrary number of those points. A handicap or "advantage" if you will. I'm sure that there would be no problem with this if nobody had to lose because of this, but there are only a certain number of seats. A seat given because of the "advantage" is a seat taken from someone else.
2. Let's assume you had to run a 100m race for entry to medical school. 1 on 1. You're opponent was fast just like you are fast, but they start 20 m ahead of you. You lose. You go shake there hand without any feeling of animosity?
Now well you can say that being an URM means that figuratively "the runner is slower", life has been harder to the URM and had to do more. Basically they have weights on their feet. Well, I'm telling you that many, MANY, of these URM's do not have weights on their feet. Many in fact actually start from better positions than many of their "over-represented" counterparts, yet still gain the advantage based SOLELY on race/color of their skin. While this may be what the schools want, one can certainly understand the "anti-URM sentiment" as was originally posed by the OP.
As a future physician, if you can't understand the very basic emotion behind what the runner who lost was feeling well then.. medicine is going to be interesting for you.