I don't cook meat for myself, but if I am at someone's house where they are serving meat I will usually eat it, with the exception of veal (for moral reasons) and ham (because it tasted gross).

The fact that a fair number of people don't eat meat DOES make a difference. Just because one person doesn't eat a steak doesn't mean another person is going ot eat an extra one in their place. By not buying meat, even a single person reduces the demand slightly. The more the demand for meat is reduced, the less meat will be produced.