Yes, police departments should be banned from tracking social media activity because it is an invasion of privacy for them to see what people see to their friends. This is like George Orwell's novel, 1984. Once the politicians and police can see everything that the people do, chaos will ensue.
Seattle police (and many other cities across the country) are using technical loopholes to be able to investigate people without probable cause. Police should have something better to do than search Facebook for pictures of underaged kids drinking over the weekend. It's just another instance of police doing what's easy, not what's right.
No. Social media is known to be responsible for a number of modern society's problems; it could be used in a more beneficial way, such as tracking illegal activity. Criminals have become comfortable with "gloating" about their exploits online. They do not seem to realize that their status updates, Tweets, and blog posts can be easily seen by almost anyone. If important information about criminals is being publicly broadcast, the police have a right to utilize that information.
Tracking social media posts are one way to monitor hate groups and hopefully forestall violent activity before it happens. These days a lot of hate groups post on social media, and some of the individuals who have committed violent crimes have left clues of a sort in their social media posts. Honestly if you're posting on social media, there's a limit to how much privacy you can expect, and stopping a crime, hate crime or gang activity is worth it.