I think that we forget how to be human, after awhile.
Our feelings harden, due to the other non human beings who cause us to build
walls. These walls tend to keep out the actual humans who, just maybe, love us.
The innocent who, just maybe, love us are also hardened because of the
inhumane treatment put on upon by the first party.
In conclusion: This goes around and around and around. Humans causing each
other to hate, fear, and harden.