You can be sceptical about the calculus, whilestill accepting that some acts usually lead to a reduction in happiness, and therefore should be forbidden, while other lead to an increase in it, and should be encouraged. The point is that the maximisation of happiness is the goal, not something else such as obeying the supposed commands of God, even if some of them lead to misery (such as making homosexual acts illegal), or maximising some other supposed good, rather than happiness.