That is a moral reason not to use one.
Those who can not stomach the horrors of real war will quickly be butchered by those who can.
We are not willing to be butchered in order to pretend to be superior moral beings.
I'm not sure I agree. These so-called peaceful iranians are doing nothing to stop the madman who has troops at israel's border and who are lobbing missiles into israel. So I don't count them as innocents.
Also, we don't have to use a nuke that destroys the entire metropolitan area, just a small one that destroys the core seat of government where this nutjob and mullahs sit. Granted there would be some fallout, but most would live.