Alternatively – there can never be a truly altruistic act.
The argument is circular and is anticipated in the maxim “virtue is its own reward”.
Theories of virtue do not exclude reward – instead they claim that some rewards are good others are not. Few such systems would regard public praise as a fitting goal of virtuous action. The cynic denys “higher” motivations, or has a world view incapable of accommodating the possibilty of a moral dimension.
If a moral dimension is denied then no judgement of the morality of action is possible.