Well, it's time to show my colors.
Frank, I agree 100% with you. I don't see how cropping an image is any different from the other processes you mention. Whether it's by viewfinder, easel or computer, it's all the same IMHO. You are merely controlling how much of a scene the viewer is allowed to see.
Although I much prefer to try and compose the image in the viewfinder the way I'd like to see the final print (or scan), I'll happily crop if it strengthens the image.
The impression I get from some of the photographers that shoot exclusively full frame is that they think cropping is somehow "cheating" or "being lazy". And I suppose this could be true of some people. But I'd like to think that most seriously minded photographers take care to compose their shots carefully, when possible.
I know it's pretty common in photo courses to not allow cropping on the assignments. And, from a teaching perspective, that's perfectly valid. After all, you are trying to teach careful composition and visualization of the final print. But to somehow extrapolate this to all image making seems to be a logical fallacy, in my view.
One of the other things I've seen (and I'd be lying if I didn't admit to falling victim myself on ocassion) is an image that could really benefit from a crop - typically because of a distracting object near the edge of the frame, where the photographer insists on not cropping it. Personal preference, of course, but I can't help thinking that by being so mired in the "full frame mystique" the photographer has somehow managed to convince him or herself that the distracting object actually makes the shot better.