See, the thing is, I used to be strongly on the other side of the fence on this issue. I used to agree with the DM's World POV. Then, well, I started trusting my players more.
Take the oft used "no evils". It's repeated so often that it's become a truism - evil campaigns can't function, they fall apart, they don't work. And, I bought into that line of thinking for a long time. I up front banned evil characters for years.
Then, as an experiment, I told the group that I was going to relax the alignment restrictions. It was up to the players to figure out how to work together but, otherwise, any alignment was on the table.
Turns out that evil groups function FAR more effectively than good ones. First off, there's none of the disrespect between the PC's. When you know that that lipping off to the other PC might cause that character to kill you in your sleep, everyone got a LOT more polite. Almost movie mafia type behavior where everyone was respectful and polite, at least to each other's faces. Then, they quickly realized that together they could succeed at their own individual goals faster and better than they could alone. They banded together for protection because they knew that not only did the bad guys want them dead, the good guys probably did too.
After that campaign, I no longer have alignment restrictions in my games. Evil characters, played intelligently, function perfectly well in a good group. And it creates all sorts of interesting interplay between the characters.
So, yes, I came to the conclusion of "trust your players over your own preferences" through experience. Your own preferences and assumptions likely have never really been tested. Let them go and your game will be a lot more fun.