In universe they are justified because Tyranids.
Tyranids won’t just kill every person on a planet, they will eat everyone, every animal, every tree, every insect and strip a planet back to the minerals and then do it again. They arent immoral because they have no morals.
In the face of that literally anything is justified even if it’s horrific.
Now in fairness we dont know how high end this Sushi place is, if its a place where your paying for the experience its more understandable but It does read a little bit passive agressive.