First of all, sentience of beings is not a necessary condition for the simulation to be borderline unethical. No other species on our planet is sentient, yet many people don't consider hurting these for fun to be moral.

I was joking of course, the joke being that ability to recognize itself in the mirror is a common test of self-awareness used by biologists. And Sims can (sort of) do that.

But! You mention "simple tricks", and it reminded me of Dan Dennett lecture on "Magic and Consciousness": http://www.youtube.com/watch?v=3jBUtKYRxnA

His point is exactly that maybe the consciousness is just a collection of "simple tricks", which, to us, give the illusion they are not so simple.

What ever civilization that runs our simulation could have drawn a distinction culturally/legally between their real sentience and sentience in their simulation. Linking and granting rights to a simulated sentience isn't a guaranteed step after all.