Even if everyone who eats meat ate it in the same way (as a luxury) it would do little to put a dent in the industry and environmental impacts. The beef industry is sourced by the dairy industry. Even ensuring that the luxury meat is only sourced from 'ethically raised' cows does not account for the myriad ways the dairy industry uses animal parts. Not just skin for leather, but bones for refining sugar, eggs as binders for many dry goods, etc. I think the only way to move forward is to completely break the cycles and remove animals from our food production processes. It would have direct impact on the environment, pollution, health (we are shielded from the amount of chemicals in our dairy/meat).

When the aliens come I don't think they'll be too surprised at seeing humans committing violence against each other through wars, but will marvel at the extremely inefficient way we use animals for food.