The argument we would be making is that the benefit of more race/species diversity outweighs the development cost. You can disagree with the value of adding diversity, but simply saying "but it doesn't come free" is redundant. Everyone knows that.
Personally, I think that orcs (or half-orcs) are core to D&D and provides substantial value to the game. We can also argue about the value added by other races/species.
I think the value added by "half" races in particular is minimal. If you like both elves and humans, then just pick one. Instead of spending time developing half-elves, we could have something more unique instead.
If you're satisfied with the current set of races and feel that they should focus development on other features, then fine. Make your case. Some of these arguments are just lazy "status quo good".
