You're arguing it's a matter of degree. To some extent I agree with you. To a greater extent it's about possession. Persians are allowed to argue about the authenticity of Persian restaurants in Los Angeles. They are allowed to support or slag as they see fit. As a white guy, I'm not entitled to an opinion. Buddy of mine isn't either - because only his mom is Persian.
That's my whole point: maybe you got no beef with appropriating cultural elements with respect, but somebody does, and they will be vocal, and they will accuse you of oppression for the simple reason that you're appropriating. Simply put: you are allowed to assist your friends in appreciation only of those elements you are entitled to by birth (not even by blood).
Yeah, unfortunately there is no handbook to culture that anyone can point to and say they are abiding by. I would argue there is zero wrong with enjoying or criticizing a restaurant because it's a restaurant and public criticism or acclaim comes with the business. I can also say a Japanese restaurant might be overpriced or a Mexican place salts their food too much for my liking. Or even that I prefer to avoid all Chinese food because it sits heavy in my stomach. All okay because it's all relative to me: "I don't like this", rather than absolute: "This is bad and a poor representation of True X Food." Then there's the grey area where a white person who has never been to Iran opening up a Kabob joint because they love the food and it's good business. As an also-half-persian, I have no problem with this, but would probably say the politically correct thing to do would be to call it "Kabobs" and not "Persian cuisine". In the former case, you are saying: "I am making this food" rather than "I am representing this culture". Annoyingly, this is a subject where the stakes are unbalanced and if you're right, it's no harm done, and if you're wrong, you're a grade-A asshole. I have the feeling social liberalism and political correctness will eventually settle on a consistent set of rules. But for now, yeah, degrees, possession, and respect.
I think it will always be "I reserve my right to be offended by any attempt you make to reference my culture for the simple reason that it's mine, not yours." And that's why the whole fucking thing bugs me. It really comes down to this: Do you want to be pissed off at me? Well guess what. You're going to find an excuse. Do you not want to be pissed off at me? Well guess what. There are ample reasons to excuse my behavior. But what it really comes down to? The argument that you are somehow justified in shitting on me for multiculturalism because something something birthright. And there's nothing clever about it, there's nothing avoidable about it, and anybody who has 50.0001% of something is gonna get shit on by the guy with 49.9999% of something because that's how we, as humans, do it.