What if Tay's AI Turned Into Joseph Gerbels?

Tay and Mountain Dew's new soda flavor vote were cases where any of us in 2012 or early 2016 would have said, we're going to do this. What if another company built an AI that learned in a way that wasn't public facing? And what if that company trusted the AI to handle a crucial task that operated behind the scenes? I think it might look an awful lot like what we've seen happen to YouTube's recommendation algorithm.