I think you are dead-on on this. While I’m in the “let the chef do what they think is best” camp, I also think what’s presented in the OP is a little bit of a false dichotomy (which is why I voted “somewhere in between.”)
Yes, it would be acceptable. Yes, the chef could refuse. Yes, you could then leave the restaurant without ordering anything.
People who say the chef should accommodate you are wrong. People who say you shouldn’t ask the chef for accommodations are wrong. There’s no “should” in this situation until an order has been made and accepted.
Quoth Left Hand of Dorkness:
Well, obviously Michelangelo can’t get any feedback from us, and I acknowledged that full two-way communication isn’t always possible. But you can bet that any artist you’ve ever heard of has had a lot of feedback from other folks. Even if they go down into the basement to paint or whatever in secret, and only reveal the work when it’s done, they’ve still had feedback as to what folks responded to in their previous works, and how folks have responded to works by other artists.
This is true. What I’m saying is that there’s nothing intrinsic in artwork that makes it better if the audience and the artist are in communication; on the contrary, it’s a peculiarly unidirectional form of communication in many instances.
Of course it’s acceptable to ask. And there’s no need for anybody involved to be a douche about it.
CUSTOMER: This dish looks fantastic, but I really don’t care for blue cheese. Can that be left out, or substituted with anything?
SERVER: I’d be happy to ask about that.
(time passes)
SERVER: The chef says that’s not a problem at all.
OR
SERVER: The chef thinks the blue cheese is a really important part of that dish, and that he wouldn’t feel right serving it without it. Can I suggest a different entree?
OR
SERVER: The chef says he could try it with a different cheese, like a fresh chevre.
A reluctance to make changes doesn’t necessarily mean that the chef is a diva who can’t stand to see his creation bastardized. It could just be that it’s a composed dish that he considers good enough to put his name on and charge good money for, and he thinks if you take off that one component it’s not going to be anything special. He doesn’t want you leaving disappointed, and telling people that the food was meh. Sometimes it really is one little thing that takes a dish from good to great, and if that happens to be the thing you asked the chef to leave off, wouldn’t you rather he tell you that than to just serve it to you and take your money for something he considers less than great?