it depends how and why they're devaluing the other human. If they're basing it on dehumanization in order to exploit/abuse them, then that is in fact built on the underlying assumption that nonhumans are fair game to exploit/abuse, although they are also factually incorrect about the other humans humanity.

Strategically, it might be easier to get them to recognize that fact, or it might be easier to get them to accept compassion for all sentient beings and then point out the logical conclusions of that, it really depends on the person and situation, but I'm not talking strategy I'm just pointing out an often-unspoken root problem