I don't think anybody advocates that a take has to be perfect and that there should never-ever be punches or other editing. In fact, sometimes "perfect takes" are those that are not technically perfect.
It's a matter of quantity and intent.
Personally I think that if a player isn't capable of getting a keeper take - it doesn't have to be technically perfect, but at least one good enough to use - in three takes, then they are either just having a bad day or not yet ready to record and should go back and practice some more. Either way they should come back and try it again another day.
I also know that many folks consider that a harsh view to take. I get that. But I'm using that here just as a starting example to make this point: there's a difference between editing someone who *can* make an unedited "keeper" take but just hasn't quite hit it yet, and editing someone who could not make a keeper take if you gave them a full day and all night of takes to do it. Editing the first guy is OK. The second guy is simply hitting the red button too early and should walk away even if their performances could be "fixed" in editing.
Now, we may not all agree on the three take rule as the line in the sand, but the line needs to be drawn somewhere. It really just boils down to the fact that one can pretty much tell if the guy (or gal) can actually play their part or not, if they're ready or not. If they can play and are ready, there's nothing wrong with a little editing to help them out with some honest issues. If they simply can't play the part well enough to actually have it stick to tape after a reasonable amount of time, then they should hold off on the recording altogether and not lean on editing to make it sound like thy can actually play.
G.