But that's what we're talking about by allowing everything in the core, all the time. It's kitchen sinking every campaign world. Dark Sun with dragonboob PCs. Ravenloft with dragonboob PCs. Etcetera.
No, not at all. A good example is muls, half-dwarves, from Dark Sun. They are an iconic race of the setting and help define the feel of it. If I allow half-dwarves in my home game, am I somehow making it just like Dark Sun? Of course not.
I allow anything and everything within the rules into my game. That doesn't make my game world identical to any other, nor does it make a kitchen sink world. I allow dragonborn, but nobody's asked to play one yet and as so they don't exist in my world . . . yet. If and when somebody asks, I'll allow them and I'm not really worried about diluting the purity of my world. Same goes for goliaths, wardens, invokers and other bits too.
If I created kingdoms and huge backstories for every race and class in my game that closely mirrored WotC's stuff, then that might start to make my world to look a little unfocused and kitchen-sink-esque . . . but even in that case, so what? I'm not writing novels in this setting, I'm running a table-top game for my friends every other week or so.
I've seen closed DM's shut down player ideas often enough in my gaming career, and I find it anti-fun for the most part. I love GMs who are open, because it frees everybody at the table to just relax and have fun! It's only a game afterall!
I do draw the line sometimes at player-created classes and races unless I trust the player to come up with something balanced. But I rarely outright say "no", I'd rather work with the player to rework the class or race (or feat or whatever) that to simply ban it.