1) There aren't many things I know about but moral philosophy is one of them having studied it for about 10 years now. Never specialised in meta-ethics but I do like to thing I have a good grasp of the basics. That wikipedia entry isn't the worst thing I've seen but it does contains some problematic stuff. The talk of moral naturalism and ethical subjectivism are, at least, very unhelpful.
Thankfully there is an excellent free encyclopedia for such things which I would recommend you use instead (the material is of the highest quality and it is the first place most professional philosophers will look on subjects they don't know about http://plato.stanford.edu/entries/moral-anti-realism/
2) I'm actually an anti-realist myself (specificially I'm a non-cognitivist, probably some sort of expressivist which is a modern version of emotivism) but still an ethical vegan
In my view (which is mostly just Sartre and Camus) Ethics boils down to a question about 'what sort of person do you want to be?' and I'm willing to make the empirical bet that with most human beings the answers to that will involve heavy overlap. Where people's answers to that question are pretty monstrous (e.g. I want to be the person that hurts the most people) then we lock them up (if they are dangerous) and/or morally condemn them because valuing certain things morally requires (sometimes) condemning certain things.
3) Whether someone is a moral realist OR
an anti realist you will often get to a point where arguments just fail because all there is is your assertion and their assertion. This, however, isn't anything bad about morality, this is just how reasoning in general works. A chain of justification/reasoning can't go on forever (well most of us think this ... a tiny minority of 'infinitists' i think believe it can). It either ends in a bedrock of beliefs that are taken on faith/self-justifying or there is an interlocking web of beliefs that all support each other or *fill in the blank*. In the latter case, however, the problem is just pushed back a step. Assuming mine and a Nazi both have entirely coherent belief webs how do we choose between the two webs?
So yeah basically all you can do when you get to this point is appeal to them to see the world in a particular way which is what etherspin is doing
Myself I would just drop all the talk of right/good/value for a moment and just talk to them about what sort of person do they want to be (it's is possible that their answer won't involve ethics but i think this is rare). Also note again that this is not a weird feature of ethics but a feature of reasoning in general.important
: note that i'm not saying all discussion of ethics is like this. If you share even one premise with the person you can do a lot in terms of argumentation. The situation I'm talking about is where there are no shared premises between the two people talking.
I'll maybe write more if I think of something I left out
edited to add the *fill in the blank* bit as I realised I was talking as though the bed rock is true or false.
JS - They think it will open the door to folk like LordMuppet campaigning for a threeway?