Arnold at EconLog has a very nice post  on the environmental impact of dogs:
Which do you think takes a bigger toll on the environment, owning a
dog, or owning an SUV? My bet would be on the dog. I’m thinking of all
of the resources that go into dog food.
You could argue that children also consume a lot of resources, but
that is different. A dog does not have the potential to discover a cure
for cancer. A dog is not going to provide for you in your old age.
I personally have nothing against dogs. But it does seem to me that
environmentalism inevitably points toward a policy of extermination of
pet dogs. Unless environmentalism is simply hatred of industry.
What’s particularly interesting are the comments. People are angry. Dogs are great, they say. They make people’s lives better.
No doubt. So do SUVs. So do grapes from Chile. I think Arnold was merely suggesting that there are tradeoffs. If you make tradeoffs for dogs (which of course you should), why not make them for SUVs?