Because suggesting outright premeditated killing for people with a given trait, regardless of whether they have actually offended in any way or are an active threat or whether killing them is the only way to stop them being one, is kinda genocidal. We should never advocate killing people for things they cannot control.

Killing someone is, as our technology goes today, final. It robs them of all potential, all freedom, of the most basic human right: life. It is a heartless thing to do to someone, regardless of motivation. Yes, when you're under attack, killing your attacker is valid, but it should never be taken lightly and inherently devalues their life in favour of your own survival. It is a trade we should accept, but also be aware of.

But reflexively resorting to murder when there is no immediate need for it infringes on fundamental human rights. And doing so indiscriminately for a psychological condition is, quite frankly, no better than killing people for their ethnicity or religion.

Restrict them from seeking power for a fundamental incompatibility with the requirements for empathetic governance, but do not call for their death. Do not forsake your own empathy.