I believe genetics play a major role, but environment is more influential since it installs the buttons that are pushed, often, for the rest of our lives, even in those that are adopted. Additionally, environment can play a very effective role in changing genetics when one has had enough and...
I think that's more of a health issue than a vegetarian/anti-meat/political issue.
For many it probably also has to do with self-sustaining food supplies as well, which is a responsibility issue.
Kenny Rogers said it best...
You've gotta know when to hold em, know when to fold em, know when to walk away and know when to run!
You never count your money while you're sittin at the table, there'll be time enough for countin when the dealins done.