Yes,disgusted because it wouldn't make my life easier. In the situation I described meeying tje source preferences would be easier (and more pleasant). Deciding for me that I can't get the salmon is paternalistic. If it does turn out to be a burden, I can make figure out that vegetarian is an option. Let me as the host decide which is easier for me.
But it might not be a simple case. For example, what if I would only eat line caught, wild fish, and only certain species at that?
I just can't think of a way to communicate that to a host that wouldn't sound like, "well, I do eat fish, but not the kind you would ordinarily buy, because I think differently to you". Heck, I get enough side-eye for saying that I don't eat meat (people feel judged when you make different moral choices, which I understand, but still). Once I've opened that can of worms, it seems safest just to keep other restrictions down to a minimum.
It seems like there's the potential for offence whatever I do. Pity.
What a horribly nasty thing to think about your friends. And how very self-centered a thought process. How do you know you are the only person who cares? (FYI - I bet you are not.) Lots of people do try to shop ethically and plenty more are willing to give it a go once in a while for a situation like a party. When someone is a friend, give them the benefit of doubt to at least try to accommodate (by for example, saying "mostly vegetarian").
I agree with Sharnita's point, just saying "vegetarian" is not necessarily the "easier" option for the dinner party host. And not because the host has "a really poor imagination, or very limited culinary experience" but because the host has other guests to accommodate as well, and they have preferences and food limits themselves.
I think you misunderstand me, I definitely don't think that about my friends, in fact I was specifically trying not to make a value judgement. I know plenty of people who feel like I do about food, and also plenty who don't.
What I meant to say was that, if somebody shops a certain way, they have their reasons for doing so. Maybe the reasons are purely financial, maybe they don't have the time or inclination to shop around for food, maybe they genuinely don't care if what they eat is factory farmed. Maybe they don't think about the origin of what they eat at all. Whatever, it's not my place to judge anybody for how they eat.
The conundrum is in how to communicate your dietary preferences without
it coming off as a judgement of your host's usual shopping practices. Because, essentially, what you are saying is "what you would usually buy is not something I'm comfortable with eating, so I need to let you know what I am
comfortable with eating". Most people wouldn't hear it that way, but some would, I'm sure.
Which is why I find it easier all round to say that I'd prefer to eat veggie. And I will say, "if it's easier, I can bring something"*, just in case that makes it harder to accommodate other guests. Although to be honest, I've never come across somebody who has medical or ethical reasons for not
eating veggie for one meal. If it would significantly impact some guests' enjoyment of the meal to go without meat or fish, I assume the host could take me up on my offer if they wanted to, or just feed me the non-meat parts of the meal. I do confess to not understanding people who just won't enjoy a meal without meat or fish, when there are so many delicious veggie options out there, but there you go.
* In fact, I'll usually say, "I don't eat meat, but I don't want to put you to any trouble", and the host will usually say, "Oh, well, there'll be X, Y and Z dishes", and I say, "Perfect, sounds delicious", and everybody is happy.