That's the way their own evolution brought them to be.
In our case we developed our brain efficiently and could evolve differently.
So, it is still unfair putting a lion against an armed man. To be a fair match, both beings must be ONLY with their own genetics.
Also, what about someone comes at your place, takes you down forcing you to have a cage death fight with another human being, only for his/her own pleasure? Would you like that?
The point is simply this, animals must be respected.