Imagine assigning every single living human being a dedicated 24/7 con artist to follow them around and convince them of something. That's what will soon be possible if not already. It will be intimate con artistry at scale driven by big data, a massive DDOS attack on human cognition and our ability to conduct any form of honest discourse.
What hustlers, trolls, and completely amoral companies will do is bad enough. Now throw in state sponsored intelligence agencies, propaganda farms, militaries, special interest groups, and political parties.
Usually I'm anything but a luddite, but with this I can't help but think of many more evil uses than good ones. It doesn't help that the principal business models of the (consumer) Internet seem to center around surveillance, advertising, propaganda, and addictive forms of entertainment (like slot-machine-like mobile games) designed to suck money or time out of people.
Lesser but also very bad concerns include: the end of useful search engines due to a deluge of continuously learning adversarial SEO spam, the collapse of pretty much any open online forum due to same, and addictive "virtual friend" / "virtual relationship partner" hyper-sophisticated chatbots that hook vulnerable lonely people and then empty their bank accounts in various ways.
I really don't fear AI itself. I fear what human beings will do with AI.