Serious answer? The greatest downside to the Internet is probably the breakdown of privacy it creates in our daily lives.

My first example is Photos and Videos. If you were born before 1990 you probably grew up with the mindset that you don't post someone else's photos online without their permission, because once it's on the Internet it is no longer yours. Now kids grow up with their entire lives documented in the public domain for all to see and that just becomes "the norm".

Another example is gaming. A lot of games these days (or gaming platforms such as Steam) announce your presence either publicly or to your friends list. Look at how frequently an "offline mode" has been requested for League of Legends by players who just want to play a game by themselves in peace without having to explain to their friends why they don't want to play together right now. On the mobile platforms, especially, games often do not work unless you are connected to the Internet, and many will attempt to share your activity on every possible social media outlet that they can.

The third and most pervasive example is cell phones. Unless you go to the extra trouble of shutting off and disabling a lot of this stuff your phone will do many of these and more:

• Tag your location in all of your photos
• Automatically upload those photos the moment you take them
• Tell your friends whether you are online and reading their messages or responding to them in apps like Hangouts and SnapChat, or tell them how long ago you were last seen using said app.
• Report your location back to Google or Apple and maintain a location history
• Send a copy of your contact list back to Google/Apple and allow other apps to probe it and use it to share your activity.
• Use your phone to push advertisements based on things like your search phrases, installed applications, and more.

Basically your phone catalogs your entire life if you let it, and most of it gets shared with companies so they can advertise to you. It takes a great deal of effort on the user's part to disable and block this sort of activity, and the common attitude is not "this should be opt-in", but rather "I don't care."

It's not just a matter of the Internet making privacy more difficult to achieve, it's causing a shift in the mindset of the general population where the lack of privacy is becoming more and more acceptable.