One thing bother me about utilitarianism is the a priori claim that this can be known without evidence that this is a true good. Many people in our day, because of lack of proper education, hold this theory to be "modern" and "self evident", which it is not.
The best critique I saw on it was from Michael Huemer but he only mentioned a few of his idea in passing without expanding on them.
I think many Jews and Christians just don't understand how different the morality of the Torah is from utilitarianism.
I should admit that when I read John Stuart Mill I was impressed. II am really not much of an analytic thinker. Only after a long time of thinking about something do the problems start to become apparent to me. and I alway like to give everyone the the benefit of a doubt.
Nowadays there is also a kind of Orthodox Jewish utilitarianism. This is that people judge other people based on whether they are a potential benefit for the super-organism of Orthodox Judaism.
Orthodox Jewish utilitarianism at first seem to propound act-utilitarianism (act in a way that brings the greatest benefit to the super-organism of Orthodox Judaism), but then when it comes to explaining why we should follow the principles of halacha, they resort to the claim that these laws, if adopted as general rules, promote the greatest spiritual good. The problem is simply the argument is self contradictory.
For the thinking person the claims of Orthodox Judaism simply seem incoherent and has little to do with the actual moral principles of the Torah.
Philo Gabriel: The verdict of most philosophers is that utilitarianism is not able to completely overcome all objections, that while the total happiness contained in the consequences of acts surely is of moral importance, it probably fails to contain everything that is of moral importance. Hence most present day moral philosophers argue for a mixed theory that contains both consequentialist and non-consequentialist elements. But the debate continues.[http://www.helium.com/items/1744710-utilitarianism-criticisms-and-responses?page=6]