GreenGenes,
When someone asks why I'm vegetarian, I usually tell them "all of the above"

In the past this has given me some strange looks but recently I had a discussion with someone who knowingly nodded and smiled and talked about how she's considered it but her husband is very pro-meat and about how sometimes she just slips it to the dog under the table, lol. It was wonderful talking to someone who actually
admired my standpoint instead of criticizing it. I love how times are changing.
I always have been somewhat of an environmentalist, I absolutely adore animals, and I care about my health as well. There are far more reasons for me to be vegetarian than not to be one. I started experimenting with vegetarianism when I was a teenager. I have now consistantly been vegetarian for about 8+ years, but about 10 total (which is over 1/3 of my life

)
In fact, meat isn't the slightest bit tempting anymore. Dairy on the other hand I'm still learning how to "just say no." I've read enough literature to know it isn't good for me, and that consuming dairy is just as bad for animals and the environment as consuming meat, but it is taking some work getting past those years of advertisement (and experiences) of pizza as the ultimate comfort food. I've been McDougalling since January first (minus a few setbacks, most of them in a rebellious one week period) and while it is relatively easy for me to turn down the greasy foods and eggs, I still find it difficult to not want dairy. I'm sure someday I'll get to a point where I find dairy as repulsive as meat but, just like switching to vegetarian, I'm sure that may take a little while.
Back to topic though, I think the most productive thing you can do when having a discussion with a meat-eater, is to not criticize their point of view. If you do, that will instantly make them defensive and you'll get an earful about how "wrong" you are. If they understand that they aren't being attacked for their ways (even though this more than often starts out as them attacking your view) then they seem to be SO much more open to discussion and may actually learn something. People are often times critical of me until I tell them my husband eats meat. Then they actually stop and listen. Now, my husband on the other hand LOVES a burger, however he doesn't buy it and bring it home. He only eats meat when eating out of the house...so he eats vegetarian 9 days out of 10. Which is an amazing step in the right direction since before me, he considered a vegetable to be a bag of sour cream and onion potato chips,
Wow that was an earful! Best of luck in your discussions with friends and family!
Alyssa