Callous or not, it's hard to justify trials ethically for that reason. Yes, it would be better for society as a whole, even if it could potentially be worse for an individual; but is it ethically right to burn up an individual for the sake of society? And now if you'll excuse me, I have to walk away from Omelas.

Edit: Pre-empting a question: Yes, I walk. I recognize that the trolley would be quicker.