I'd rather have one idiot on the case than that idiot + a bunch of other, self-selected idiots prompted to show up by an app. At worst they will actually hinder police response and/or get themselves or others hurt.

Keep in mind that the user base of Citizen is not a uniform distribution of the population either - certain classes (for the lack of a better word) will self-select and are likely to have similar issues to the police itself. In fact you might have the kind of people who can't even make the cut to join the police itself, which is not a good thing when you see how low the bar for the police is to begin with.