Final answer:
The serious charge against the adequacy of act-utilitarianism is that it can undermine our considered judgments about justice and rights by justifying actions based solely on consequences, often at the expense of individual rights or fairness.
Step-by-step explanation:
One serious charge against the adequacy of act-utilitarianism is that it flies in the face of our considered moral judgments concerning issues of justice and rights. Act-utilitarianism proposes that people should always perform actions that maximize happiness or utility, even if it conflicts with our significant moral intuitions and considerations about justice and individual rights. Critics argue that act-utilitarianism, by focusing solely on the outcomes or consequences of actions, can potentially justify actions that are widely seen as unjust or wrong, such as punishing an innocent person or violating individual rights, as long as such actions would lead to the greatest overall good.
In contrast, other ethical frameworks like Kantian ethics, rule-utilitarianism, and virtue ethics attempt to incorporate or protect certain moral rights or duties and thus are often seen as better aligned with our considered moral judgments. Act-utilitarianism's tendency to override individual rights for the sake of aggregate utility is its primary shortfall according to its critics. This fundamental critique of act-utilitarianism reveals a tension between individual justice/rights and the pursuit of overall happiness in ethical considerations.