The way I interpret her words is that there is a simple honesty in those who do good things for others' approval. Contrary to people who do good things based on their own morality, which may be much more complicated and convoluted. It is not to be taken as the truth, and there are sufficient examples pro and contra either way.
Also, most likely she is joking around her words are not to be taken at face value. Remember this is a flirty conversation with her husband, not a deep philosophical dive.