The argument was that because both are alive they are morally equivalent. This is specious because humans are also alive, and are clearly not equivalent to eith

The argument was that because both are alive they are morally equivalent. This is specious because humans are also alive, and are clearly not equivalent to either unless you accept that it would be acceptable to kill and eat humans. It's not as stupid an argument as "but People!", it's pointing out that they are neglecting other variables, such as the capacity for experience.