Mostly, we don’t think too deeply about the things we do. We do them for various reasons. Tradition and fashion, though apparently and sometimes genuinely in conflict, are common motivators for our behaviors and actions.
We paint the house in subdued colors if the other houses on the street are painted in subdued colors. We wear clothes similar to the clothes others are wearing, style our hair similarly, and eat similar foods. We sometimes, sometimes habitually, choose to do things that make us feel good, like eating a favorite food.
Seldom do we do these things with much introspection or questioning.
People eat animals for two reasons. Eating them is a tradition, and we have developed a taste for their flesh and secretions. These are relatively trivial reasons when weighed against the suffering inherent in animal agriculture.
Usually, when people pause to consider this equation they come up with a few other possible reasons for eating animals, but none of them have much weight unless, perhaps, one is an Inuit or a Kalahari bushman with no access to grocery stores. For most people, tradition and gustatory delight are adequate reasons to keep eating them.
If the suffering inherent in eating beef, pork, poultry, and fish is justified with such trivialities then no real consideration of other uses of animals seems possible. This explains why the vivisector with the monkey strapped into the chair is so confused by the public’s complaints and concerns. If tradition and flavor are believed to be reason enough to keep animals in miserable conditions and to treat them poorly and kill them, then surely they can be sacrificed on the alter of scientific knowledge without qualm.
If you sit in the stands and eat a hotdog, how could you care about a terrified calf being roped around the neck and slammed to the ground?
Discussions about animal use in science and entertainment are hard to have with people who believe their tasty fat is reason enough to make their lives hell.