Gay marriage is not the "civil rights issue of our time"; I wonder if gay marriage will even get a footnote. Just in terms of scale, the issue of our treatment of non-human animals in the last century is so much more massive than any grievance of any sexual minority. History will judge this age by the way we are treating the animals who trust us to care for them. I've said this before.
We've all read Omnivore's Dilemma by now, we know that the way animals are raised for meat these days is a nightmare. But this is just as monstrous. In fact, I would say it's worse because it's not the behavior of some impenetrable corporate bureaucracy whose power over our lives we don't understand and feel powerless to affect. This is just folks. It's one thing to turn a blind eye to the provenance of that McDonalds burger you eat every day for lunch, quite another thing to seek out a breeder, buy a puppy, then drop it off at a shelter (or in the highway median) when it's not cute anymore. That is a degree of baldfaced evil that I can hardly imagine being capable of, yet people do it every day.
I think I'm a pretty reasonable person. I'm not some howling PETA activist or radical vegan. I'm not even a vegetarian. I understand that things die so other things can eat. In fact, if these people ate the chihuahuas instead of abandoning them for someone else to kill and dispose of, I would find that some degree of evil less.