Like others have said, not using horses is a cultural/learned thing more than anything else. It's hard for us to stomach eating them because we have a mythology surrounding them that makes them "different" than any other animal. That makes it a lot harder to not think about what you're doing when you're eating meat.
I love meat in general, although I don't eat a lot of poultry because I find the way they are raised to be extremely distasteful and it's difficult for me to put it out of my mind when I'm eating it. That's not an issue I generally have with most traditional meat animals and there are many people who would feel the same way about horse meat.
All of that being said, I probably won't buy horsemeat if it's in the store. When I was in Iceland I jumped to try horse tenderloin, I was completely on the "meat is meat" wagon. Was it delicious? Yes, beautifully grilled, nicely medium rare, tender, and seasoned with a delightful mixture of rosemary and other herbs. However, it was extremely difficult for me to get beyond the fact that I was eating one of those beautiful ponies I'd been squeeing over all day long.
It's just a personal thing, not something that I feel the need to impose on anyone else. I really don't understand why people continuously feel the need to impose their personal beliefs and preferences on the rest of the world.