I have no such limits. Death, as a penalty, is always unjust because humans do not have free will. Every action, every thought, has some biological, or neurochemical, or material basis for it's happening. Inflicting any form of punishment or suffering on the qualia, the conscious experience of someone, for the illusion of choice we believe to have, is actually just inflicting suffering on innocent beings, because we have no choice.
Now, that's not too say I'm anti-violence. But I firmly believe that every piece of violence should be evaluated as if it was being done against an innocent person. Things like "guilt" or "they deserve it" should not be taken into the calculation when doing violence at all, only the benefits it has to the rest of society. If you are in the position to levy death as a punishment, I would rather just see them locked up for life.
Because people like to make claims about human nature that simply aren't generally true. Rather than recognizing the way complex circumstances can shape human feelings and behaviors, I frequently see people break it down into simple platitudes like "humans are lazy, greedy, etc", rather than recognizing complex realities like the way power erodes empathy.