Why don't some people believe in utilitarianism?

Some people reject utilitarianism because they find it overly simplistic, arguing that it reduces complex moral situations to mere calculations of pleasure and pain. Critics also raise concerns about its potential to justify morally questionable actions if they result in a greater overall good, such as sacrificing individual rights for the benefit of the majority. Additionally, some believe that utilitarianism overlooks the importance of personal relationships and duties, which can lead to conclusions that conflict with deeply held ethical beliefs.