Utilitarianism is immoral

Utilitarianism teaches that what is right is what is good for the greatest number. Utilitarianism is not moralistic at all in any sense of the word. It is immoralistic. It teaches that what is right or wrong changes with the tide so how shall we say one thing is wrong and another right. Sure what is considered moral may be so now but in 10 or 100 or 1000 years down the road it may not be for we have "progressed". Utilitarianism therefore does not teach moral norms for people and is therefore harmful for society. How unfortunate that a philosophical view that teaches that what is good is what gives pleasure for the majority. I suppose we may never know what the good is. Maybe Hitler sought the good for his people by murdering several thousands or millions of Jews for his people. Today, we find religious people accepting this viewpoint also related with Christian Hedonism.