I think that they went for overkill because there was no way to develop Morgana's story slowly, and also because they can't really move on the further, more epic, development the other characters until she's gone.

If they do a reboot of ANYTHING then I am totally quitting the show. I don't think they will do that, but now you've put the thought into my head. Curse you.

I think Merlin, while not being a collaborator, actually can't see good from evil yet. Or he can't see the shades of gray to be able to easily make choices that are for the greater good.