I have been to enough GenCons, Gamexes, OrcCons, GaryCons, SoCal Smackdowns, StrategiCons, etc. to have heard things that make me ill. Again, my point, I have never heard it as advice. I have never heard another DM tell another DM they should run their game this way.
I will point out something to you and take it for what you will: Maybe it's not all the surreptitiousness and slyness that you think you see. Maybe it is you distilling someone's argument down to a sensational headline, rather than the complete depth of their claims. Just a thought.
Example 1: I have heard some people on here insist that goliaths should be stronger than halflings because of the size and weight differential. I have never seen them tell another DM they should do the same. But in the very next breath, I have heard the opponent of said DM say they obviously have a type of bigotry in their game towards smaller people. Sensational headline formed.
Example 2: I have seen many debates on here about ASIs. One DM wants to keep them. Wants to keep their smart elves and gnomes. They clearly stated others could do what they want. In the same argument, the opponent of said DM hinted at how racist it was for them to keep that rule. Sensational headline #2 formed.
Example 3: I have seen many debates about inherent evil for some races. One DM wants to keep their drow or orcs evil. They never insisted or advised others to do so. In fact, just the opposite. In the same argument, the opponent of said DM didn't hint, just stated they were racists. Sensational headline #3 formed.
These sensational headlines remove the part where the DM wasn't giving advice, but declaring how they run their table. Because that is what this whole thread is about - giving advice. And again, you can tell me all the times you have heard a racist, bigoted, misogynistic blowhard that has their head up you know what saying something while you were eavesdropping, but that doesn't make it advice. Never mind the rarity of it - which I am also willing to argue about. Because it is not nearly as prevalent as what some make it out to be.