People can't think critically over why they prefer meat over vegetables. They just think they do it because hurr durr meat tastes better or you need protines.
If they actually think about the fact that they have been eating meat for every meal since they were a child they might understand that it is just a habit they have formed.
I strongly suggest to those people to try to have 1 dinner a week without meat or fish. It has nothing todo about taste and all about habits and what you are used to.
Try to challenge yourself a little bit and you might get a better perspective over these things.