I don't know. There's a spectrum to it all and a threshold after which it tips into evil.

Hanging might be more painful than injections, but it's not quite the same as disemboweling someone or some fantastical medieval torturer drawing someone's death out over several days. Wanton cruelty is immoral, and that's what I see being advocated for. It doesn't magically become a moral act simply because it is visited upon our enemies.