To not feel bad on doing bad is bestially bad.
Suppose we accidentally step on someone’s foot. We would naturally apologize, ask if they are ok, and do what we can to help. Overall, we would feel bad if we hurt anyone.
Such remorse on doing something bad is good – it checks us from doing things that hurt others. Unfortunately, some people don’t feel bad on hurting others. If they step on someone’s foot, they blame that person for coming in their way.
How do people become so desensitized? One common reason is intense attachment to something else. Whatever we are attached to, we experience strong emotions in relation with that. And our experience of everything else is shaped by how it affects that desired object. To get it, even if we do something terrible, getting it feels so good that we don’t feel bad about our wrongdoing.
For example, some greedy people kill their competitors but feel no remorse – they feel only delight at their increased wealth (Bhagavad-gita 16.14). Their actions resemble those of bestial predators who gleefully feast on their prey.
Within us all exists a beast – our lower side that wants its own pleasure, even if this pleasure causes others pain. That beast is usually kept in leash by our conscience. But when our conscience becomes mute, that beast takes over our inner world, making us act bestially.
How can we overcome such desensitization? The most efficacious way is by practicing bhakti-yoga. To illustrate, bhakti practice transformed Valmiki from a sadistic hunter into a saint who composed the Ramayana.
How does bhakti sensitize us to others? By giving us higher fulfillment, thereby weakening our desensitizing desires; by helping us see everyone empathically, as parts of our Lord, as members of one divine family; and by increasing our receptivity to Krishna’s inner voice, which is our pure conscience.