If the 20 gauge never existed, there would probably not be a need for it to be invented.
There is nothing a 20 gauge shotgun can do that a 12 gauge cannot do with more versatility except for maybe shooting a smaller lightweight slug. I shoot 3/4 oz loads in my 1100 12 gauge for skeet (perfect), 16 yard trap (adequate) and for the first time this past weekend sporting clays (not good with an I.C. gun, but still fun). 3/4 oz is even less than 20 gauge standard loads, it's more like 28 gauge. If I wanted to shoot 7/8 oz like a 20 gauge, it would be no problem and theoretically, the pattern should have less fliers because with a shorter shot column, there will be less deformation of the pellets. That doesn't really matter to me because I shoot reclaimed shot and some of the pellets already look like cubes and others like a frisbee. I can easily hit what I need to hit when I point right and if I don't, 2 ounces of shot won't break the target.
You can always down load a 12 gauge to shoot like a 20, but you can't always up load a 20 to perform like a 12.
As a shooter, variety is the spice of life and I would never say get rid of all 20's. It's just that I doubt that I would even take a 20 gauge shotgun now if it were given to me. The amount of ammo I typically shoot is usually worth many times the value of the gun and I would not want to have to tool up for another caliber of shotshell reloading.
No real hate for the 20 gauge, just indifference like 327 Federal Magnum or 222 Remington