I think the original writer's point is more nuanced than that. A) Something that is annoying to me/that I disapprove of isn't necessarily something I consider "moral decay", if I actually think about it. B) Many of my attitudes are acquired from childhood and thus don't represent society as a whole, or anything objective–so I should be suspicious of my judgements of morality anyway. C) I don't know most of the 'annoying ambitious people' very well, and this is why the human morality-judging instinct is a misfire; yeah, if my tribe consisted of 20 people, my disapproval could have a big effect on any given person, but given the size and complexity of our current society and the number of other friends all these people have, I'm likely to have a negligible effect even on the person I'm judging, much less on society as a whole.

Your point is valid for groups that closely represent the human ancestral environment–for example, small-ish tightly knit groups of friends, like those seen in middle and high school, or among people who go to the same church. In which case disapproval of 'moral decay' does have a significant effect. But I'm not in the tight-knit circle of any of the people I disapprove(d) of.