Most people are not persons of interest and nothing particularly bad will happen to them if various entities have access to their private info. Still, they might have their identity stolen, get scammed (e.g. Dell) or pranked (e.g. swatting, disconnecting utilities) or have their house broken into if they have bad luck. They might pay a premium on insurance for having the wrong friends on FB or get fired for holding certain opinions. Might get mobbed by the internet, get harassed by salesmen or silly ads for herpes.

Let's assume for the sake of argument that the above events are unlikely though. When a few actors have access to the information of tens of thousands to billions of people though, this has an impact on a societal level. As jaquesm said, information is power and when one has so much information and lots of money to boot, they can begin to covertly influence policy and behavior and harass and marginalize their opponents. And they can do that directly, or by using the information of a third party, like a doctor, lawyer, religious leader, or even someone insignificant which happens to be a relative, etc. Moreover, companies can be sold, together with their databases, they can be forced to hand them over or they can be hacked. A treasure trove of data held by an otherwise principled company, might end up in the hands of an unsavory party.

Why is this a bad thing? History has shown again and again how such imbalances of power are abused. Here's a rather harmless example of data mining a mobile device + social network combined with social engineering to scam people out of money: http://toucharcade.com/2015/09/16/we-own-you-confessions-of-... If a game producer can do this, what are the pros doing?