If you explicitly tell someone that they're banned then they will just clear their cookies and make a new account. That's for sure.

But I don't think that justifies the act of presenting a completely false world to them in which they are active members of the community, while in reality no one can see their contributions. It just seems dishonest and contrary to the values that made the community strong in the first place.

I think it's a bad policy and should be reconsidered, even if it means that some disruptive people will be harder to get rid of (we can just keep downvoting them like we always have).