You're bordering on betraying yourself as more closeminded than those your criticise with that statement.
I'll speak for myself, though. I prefer a party of "straight" characters that throw the fantasy of the world into contrast. If the party are a bunch of monstrous characters themselves, the real monsters become all the less monstrous. I realise that dwarves and elves are arguably monstrous, but they're not traditionally presented as such, and therefore don't have that vibe about them....maybe one day warforged will enter the same category for me, but I doubt it. Then there's just the aesthetics of a "tin man" PC which grate on my nerves....in moderation it's fine, but I don't like the flavour of it 24/7 as a PC - it's too much pepper that spoils the meal.
The wannabe-doppleganger and wannabe-werewolf races also bring aesthetic problems in that they come across as "watered-down substitutes for the real thing", and because we know the behind-the-scenes reasons for why they are this way they are thus another example of the rules defining the "flavour", mystic theurge stylee, which is another thing which I have trouble swallowing.
That said, I really like the "flavour" of golems as an NPC, and think they make fantastic monsters because of the automaton quality (meaning they can be set up as part of puzzles and traps, and all that optional "becoming almost human" stuff makes them interesting).
As another example, I don't like PC psions, because I prefer psionics as an alien seasoning to the campaign for making stuff like illithids all the stranger. Psion PCs is too much of what should be a spice, IMO, just like the way that a single instance of industrial magic as an adventure hook might be cool and interesting, but too much compromises the "feel" of the game for me...or one crashed spaceship introducing laser rifles might be fine as a novelty, but pervasive laser rifles as the PC's primary weapon might be too much.
A lot of other folks are a lot more free and easy with the tone of their game, or prefer a tone where psionics and robots and magic-as-substitute-technology are centre stage....you're one of them, right?