Debating a 'moral anti-realist'?

Maybe you can assess things without using moralistic or ethical language such as "right" and "wrong". Instead just talk about the level of damage delivered onto a victim. That can't be argued. So in a country where there is no ethics or morality, you could still take someone to court and say "they caused this much damage" or "they stole this much money". You can quantify the crime without saying it is wrong.

From there you've got two options - either this isn't what a moral anti-realist would like, or it is. If it is what they'd like, then the rules can still be expanded to animals. If it isn't what they'd like, then what kind of legal system would they like? If you truly believe there is no such thing as right or wrong, how can you even have a trial? Surely such people would say that there should still be a legal system, and if so, on what grounds, and how does it function? I believe that whatever the system, it can still be expanded to incorporate animals.

But at a fundamental level, I just do not believe what a moral anti-realist is saying from the start, it seems just a cop out, a way to not worry or bother with ethics, rather than a genuine belief that they don't exist