>Innocent of anything that would merit being executed by a concerned citizen? Since when do we endorse vigilantism at all?

There's absolutely such a thing as self-defense. If a woman kills her potential rapist, she's killed a not-innocent person. We don't use the word "vigilantism" or "execution" for it, but it's a case of a person being killed by a concerned citizen where that person isn't innocent.

And even ignoring self-defense, "not innocent" doesn't mean "okay to kill them", it's more like "did something bad which increases the chance of getting killed". If a bank robber argues with another bank robber over the stolen money and gets shot, we don't call that the killing of an innocent person, even though it's not legal to shoot your partner in order to take his stolen money.