Each individual is facing the following choice in life:
sacrifice to save the planet, and fail
or not
People want to immediately jump to “if everyone would just …”
Nobody is looking at an “everyone does X” button. People only have their “I do X” button available.
So that is literally the answer to your question. Very few people would sacrifice the civilization to eat a cheeseburger. But nobody has that choice or that power in their hands. Their choice is eat the cheeseburger or not, and the survival of civilization stays rigidly the same between those two choices.
Best response. Almost everyone alive has a net negative impact on the environment. Maybe that one Indian guy who planted a whole forest by himself gets a pass. We can try to be less negatively impactful depending on our inclinations, resources, and other interests and priorities. Some people may choose vegetarianism, some might buy an electric car or install some solar panels, some might organize politically for a new policy. Some might spend their altruism improving social conditions rather than focusing on the environment. But being ever so slightly less of a negative impact on the environment than your neighbour who has a slightly different set of priorities is hardly a reason to feel morally superior.
There's truth to that. None of us is free of blame, and there's always going to be a cost associated with the luxuries and comforts that many of us enjoy; but it's not about "feeling morally superior", it's about doing the right thing, reducing unwarranted harm and suffering as much as you reasonably can. And changing your diet, eating more fruits and veggies and less meat, is probably one of the least obtrusive ways to do so (save for folks with rare medical conditions, or people who live in an environment without an abundance of arable land). Even if you don't give a shit about the suffering of animals or the environment, you at least ought to care about your own well-being.
I've eaten meat my whole life, still do... but I've cut back a lot, and it really hasn't been that difficult. Every time this conversation comes up, nothing annoys me more than the hive-mind crawling out of the woodwork to dump on vegans for daring to speak out against something that is demonstrably harmful in several ways, and then claim that vegans do it only for the purpose of moral grandstanding. Moreover, the absurd amount of appeals to nature and the lazy "bacon tasty" retorts make all of these people look like fucking dorks.
You don't have to flagellate yourself for eating meat, you don't even have to give up meat entirely... But don't be a jackass about it, acknowledge the harmful reality you're contributing to and you can either accept it for what is, cut back and reduce your contribution, or choose to lead a life that doesn't enable it at all.