No one's asking you to have sympathy. You're being asked to ignore that base part of our monkey brains that delights in hurting the people we feel deserve it for its own sake when we're talking about how to design fair and equitable systems of justice.

I have no sympathy for them either, but this isn't a genetics or upbringing thing, new broken people and new manipulative people will always be with us. There is no way to sever them from society other than resorting to the same authoritarian tactics that they use (such as murder), so it is much better to create a better society that makes their complaints about it seem as loony as they actually are. As long as there are broken people to prey on, there will be new manipulators who follow the script. For example, Donald Trump isn't actually smart enough to understand he's playing the fascist playbook, he knows it as the mob boss playbook combined with a life in which he has faced no punishment, so it stands to reason he really believes he deserves no punishment for anything he has done. He knows he did them, and just thinks they don't count as criminal acts because he did them, and he is special. A lot of his choices have more to do with his own narcissism than they have to do with genuine fascism, they just end up appearing the same. His fascist followers and enablers, on the other hand...

We can not have sympathy for them while also advocating for better prison conditions in which to lock them up. They still did wrong, they violated their own community, no less, but us resorting to their tactics means we've lost the plot, because removing our enemies from society will not suddenly make society better (or stop new people from doing the same things). We need to minimize the damage they can do, absolutely, but that can and should be done without resorting to outright removal from society. Rehabilitation may be impossible, but it should still be the goal.