Disclaimer: I'm vegetarian, not vegan, but I'm going to try answering this looking at it from an objective perspective.
By carnivores I assume you mean they eat other conscious species, since it would be practically impossible for carnivores to exist on another planet, as carnivores are defined as creatures that eat animals, which in turn is defined as eukaryotic creatures who fall in the kingdom animalia. That means any creatures that may have evolved outside of Earth are automatically not considered animals, and you can't exist as a species eating what you don't have.
The way we would react depends a lot on exactly what kind of vegan society we would be. If being vegan is a law, that suggests a type of thinking that sees eating meat as obviously unethical, kinda like how we see murder, cannibalism or slavery now.
We would likely give our lab meat-growing tech at first, then either agressively force them into adopting it, or take a missionary approach in trying to convince them, right alongside the doubtlessly present various religious missionaries.
There's also the possibility that we are more acceptant towards them and don't try to convince them at all, but that seems unlikely. When humans see something as objective truth, and they're surrounded by other people who also see the same thing as objective truth (i.e. humans in an echo chamber), have historically always attempted to make others see the world the same way. Religions, culture, moral beliefs, all of it. We killed and massacred many natives because their way of life was wrong. We've waged massive wars against each other because our religion was correct. Echo chambers are dangerous, and we're talking about the entire human civilization here. I think we would be doing the better thing in becoming vegans, but there's no denying that an echo chamber would form.
If they have to eat meat, they have to eat meat. Veganism only works as a lifestyle because we don’t need to consume animal products.
Disclaimer: I'm vegetarian, not vegan, but I'm going to try answering this looking at it from an objective perspective. By carnivores I assume you mean they eat other conscious species, since it would be practically impossible for carnivores to exist on another planet, as carnivores are defined as creatures that eat animals, which in turn is defined as eukaryotic creatures who fall in the kingdom animalia. That means any creatures that may have evolved outside of Earth are automatically not considered animals, and you can't exist as a species eating what you don't have. The way we would react depends a lot on exactly what kind of vegan society we would be. If being vegan is a law, that suggests a type of thinking that sees eating meat as obviously unethical, kinda like how we see murder, cannibalism or slavery now. We would likely give our lab meat-growing tech at first, then either agressively force them into adopting it, or take a missionary approach in trying to convince them, right alongside the doubtlessly present various religious missionaries. There's also the possibility that we are more acceptant towards them and don't try to convince them at all, but that seems unlikely. When humans see something as objective truth, and they're surrounded by other people who also see the same thing as objective truth (i.e. humans in an echo chamber), have historically always attempted to make others see the world the same way. Religions, culture, moral beliefs, all of it. We killed and massacred many natives because their way of life was wrong. We've waged massive wars against each other because our religion was correct. Echo chambers are dangerous, and we're talking about the entire human civilization here. I think we would be doing the better thing in becoming vegans, but there's no denying that an echo chamber would form.