if you go to a vegetarians house for a meal they will only serve you vegetables

This is not necessarily a bad thing. If you came to my house for a meal and I served you some meat, it might kill you. I stopped eating meat before I learned how to cook. I don't even know how to buy meat, much less cook it.

I ask the veggies to answer the question:

In terms if habitat sustainibility, which would you prefer; half of us omnivores to become vegi or all of us omnivores to eat a quarter as much meat?

I don't think it's up to me to decide what others eat, but it would seem to make more sense for many people to eat less meat than for half of the meat eaters to be forced to stop eating meat altogether.

This may seem like a half-arsed argument for keeping on eating meat, but the point is that without meat eaters amny varieties of these animals would now be extinct.

These animals wouldn't exist in their current form had they not been bred for the purpose of meat production. I don't see why their going extinct would have any discernable negative impact on the ecology of the world.