Isn't that what the US does now with death penalties imposed against convicted felons?

But our criminals are not innocent people, and that makes a difference. You might say that Saddam's people were guilty in his eyes, but that's not enough. We do not execute people for idle crimes.

So why then has the US not sorted out North Korea & Iran already [to name the "Axis of Evil" countries mentioned post 9/11]

I don't know, though it's clear we can't engage in another war. However, I'll conceed this point (see my above post).

And therefore to try and draw a line in sand between the good guys and bad guys is getting harder by the day.

Yes it is, and the U.S. has supported some very bad things. This is moot, though, in my overall point. Saddam was without question evil, no matter what we have or haven't done. If you think that badness is relative, or that what Saddam did was OK because he had the right title then you're certainly entitled to that opinion. I just disagree and believe we can call what Saddam did evil.