Several modes of attack come to mind:

1) Was hunting wrong in the cave man days? Were they evil? No? Was hunting wrong when the Indians did it 150 years ago? No? So, can you point out the date for me when, bling! the lights came on and suddenly hunting became wrong?

2) So you're a vegan, huh? Did you ever think about all the little bunnies who have to starve so you can wolf down all that salad?

3) After you've saved all the poor deer from us evil hunters, then what? What are you going to do about bears and cougars and wolves, oh my? Do you honestly believe the deer are going to love you for sparing them being shot so they can be torn apart by fang and claw instead?