What I'm arguing against is the assumption that CGI can or should completely replace using live actors at all.
Oh, I most certainly think it should not! I don't want to see a movie that completely eliminates the human element. I'm just saying that once CGI gets to the point where you can cheaply and easily replace a real human actor, Hollywood will. It goes against the mindset of business in American, especially Hollywood, to not save money by any means necessary.
It probably won't be many years until this is possible, but given how quickly CGI overtook traditional special effects and how many movies of all genres use it, I feel it is only a matter of time.