I remember going to the anti-war protests in NYC for the Iraq war and joining with some friends. I also remember coming home very disappointed, realizing that 95% of those protesting were seeking identity and using this 'cause' as a prop for that identity. And that they were engaging in the same dynamics of separation, projection, and 'us versus them' that the 'opposition' was engaging in. The end result was that there was no effort to partner with the other side and the other viewpoints and to see everyone as equal and as products of different conditioning. And this meant that we just had the same dynamics perpetuated where delusion and identity were sought without regard for achieving something real. When I brought this up to my friend, he became furious and didn't talk to me for a while (all of our egos become very very defensive when confronted with the reality of these common dynamics). I'm reminded of a Zen master telling us two stories that really stuck to me: when he was a student, he saw his enlightened zen teacher in the distance and put on a serene 'zen face'. His zen teacher saw right through it and made a puking sound which infuriated the then-student. He soon came to realize, though, how much of an identity he was seeking and came to terms with the ego and its dynamics. That same zen teacher told us that some of his students wanted to go and help out the victims of the tsunamis. Being an expert in understanding human dynamics and the ego, he advised against it, knowing that although they were convinced they were going to selflessly help, he knew that their goals were subtle supports for the 'self'.
The point of all of this is -- whatever you do, do it with a high degree of self-awareness and see if you're doing it to ease the suffering of ALL beings (sentient and non-sentient) or whether you're doing it for personal meaning and identity. Most of us do it for the latter (and delude ourselves we're doing it for the former); and the result is that we just perpetuate the dynamics that lead to all suffering in the first place. If you see meat eaters as immoral or in need of your special instruction, stop there and work on that. Only by getting rid of the ego in ourselves can we really bring change.