> what harm came from this app?

Would you say that the current political climate has been harmful? I would. I would not only say that, but I would also say that it's come about specifically because of data collection practices which have enabled data analysis of entire populations in a way which has never been seen before.

While analysis of populations is not inherently bad by itself, the outcome certainly has been, particularly because the abilities and effects are so new that there's little or no law governing people towards positive effects for society as a whole. Without those laws, the effects become geared toward benefiting people at the top either directly (company CEOs) or indirectly (capabilities sold to those who can afford them).