Sure we can!
The argument is null and void given that visual distinction already doesn’t exist.
Place a Void Elf and a Blood Elf right next to one another, then ensure they’re both using the same transmog and skin tone. Next, make them wear a helmet.
It’ll be impossible to tell which is which if you have names disabled.
There are already helpful tools in place to ensure there is no confusion even with no helmets and using the same hair styles and colors.
Depending on which faction you’re on, one of the players will have an orange name above their head. If you hover over their mode or unit frame, the tooltip will tell you which race they are (an possibly faction although that might be a Pandaren only tooltip). Their unit frame will also be a different color.
All of those things can be noticed from a large distance away as well.
There’s also the Void Elf racial Entropic Embrace, which would easily help you distinguish one from the other while they’re in combat.
So yes, you can dismiss the visual distinction argument. That doesn’t mean it’ll stop the disagreeing though.