I don’t think the evil spoken of in those verses speak to the taking of innocent life; especially if one tries to reconcile verse 18 with verses 17 and 21.
Imposing consequences for great evil is not evil.
Evil is evil, and murder is definitely evil. Whoever killed Tiller decided to play God. Tiller’s murderer was overcome with evil just as Tiller was overcome with evil. Christians are taught to pray for their enemies and to love them, not murder them.
Your point is well taken.