It's a pity that before we've even begun creating a new civilization, we've started issuing dictates. I really hope that this policy is purely for pragmatic reasons and not the personal pollitics/ideology of one person being put upon others.
Eating vegetarian is dramatically more efficient, energy wise (I'm not trying to be a vegetarian apologist here, I am quite omnivorous myself, it's just a statement of fact), and any martian colony simply won't have the resources to waste on meat.
Meat is a luxury.
Sounds like this is at least partially personal. However, there are practical reasons for this too.