I come to this question with a bias, too. I’ve been vegetarian for many years now, motivated by these same concerns. I don’t feel that this confers any moral superiority upon me; it was a personal decision and I’m not out there trying to make converts.
Most of us would agree that compassion is fundamental to any moral system. It’s our ability to look at another being and recognize that we’re not so very different in our desire and right to be free from suffering that keeps most of us from running roughshod over anyone weaker than we are. Gandhi wasn’t the first to point out that concern for the welfare of the poor and weak is the hallmark of a morally developed individual or society. Jesus said as much, as did our founding fathers. I don’t find it a stretch at all to extend that same recognition to any creature that’s capable of suffering.
The American public has developed some pretty strange behaviors with regard to animals. One striking example is our squeemishness at the idea of eating horsemeat. Plenty of other countries have no such reluctance; many european countries relish it. Why don’t we? My state, Illinois, recently outlawed the processing of horsemeat. What’s so different about a horse? The whole nation mournes a racehorse that has to be put down on the racetrack. It’s that we’ve allowed ourselves to look at it with compassion, as a kindred spirit. Same with dogs and cats, of course.
Americans have distanced themselves as far as possible from the reality of the industry that processes its meat. We don’t want to see any part of the process until the steak shows up in its plastic wrapped tray. The general outcry that greeted the leaked videos of cows being abused at the slaughterhouse is some indication of how insulated we are from the nature of that industry. We enforce that distance from the process because both we and the industry know that our compassion can be a powerful and uncomfortable force.
This is not the same as saying that animals have the same rights as people. It’s saying that it’s our capacity to want to diminish the suffering of other sentient beings that is humanity’s moral compass. To whatever extent we exclude some beings from those feelings of compassion, we confuse that compass.