Provide a comprehensive analysis of utilitarianism as an ethical framework. Discuss the core principles of act utilitarianism and rule utilitarianism. Explain how utilitarianism approaches moral decision-making and the concept of 'the greatest good for the greatest number.' Address common criticisms of utilitarian theory, including the challenges of measuring utility and potential conflicts with individual rights. Include historical perspectives from key philosophers like Jeremy Bentham and John Stuart Mill, and discuss modern applications of utilitarian thinking in contemporary ethical debates.