I think some hate them because they want the phone to be a pretty black slab. I'd rather not have anything cluttering up my screen. I want to be able to have whatever app is running take up the entire screen, and have the capacitive buttons there off the screen where I can access them at a moment's notice. At first I was interested in the LG G2's ability to customize the on screen buttons, but I really don't care. I don't care if they are customizable. I don't care if they rotate. If they are on the screen, they are in my way.
As for the capacitive buttons, the only thing that bothers me is that there is not a standard for them. They moved the back button from where it was on the RAZR. I'll get used to it, but I shouldn't have to. They also changed what the buttons were and how many. I don't get the hatred of the menu button. I was happy to see that I can set the app button to function as a menu button from a long press. Personally, I was fine whit the long press of the Home button to get recent apps, and a dedicated menu button.
It is almost as if Google wants them on screen because they don't know what buttons they want to be there, or what their train of thought will be on the next release.