Why is privacy important?
Privacy is one of the main pillars of democracy, and a fundamental human right. In fact, it is so fundamental that it's encoded in the United Nation's Universal Declaration of Human Rights, Article 12:
"No one shall be subjected to arbitrary interference with his privacy, family, home or correspondence, nor to attacks upon his honour and reputation. Everyone has the right to the protection of the law against such interference or attacks."
Large internet companies, such as Google and Facebook, make most of their money by showing you ads. In the past two decades, they have been perverting the internet to be able to track every little thing about everyone in the world, only that they can show more relevant ads, and in turn, get more money from their ad customers.
This in itself sucks. What's even worse is that organizations use this trove of data to shape public opinion in unprecedented and dangerous ways. You've probably heard of the Cambridge Analytica scandal, but this is only the tip of the iceberg. Even without obtaining user data illegally, organization can micro-target people, knowing exactly what to tell them to influence their opinions based on psychological profiles build based on this data.
One can only imagine how this type of data can be used even more malignantly if accessed by truly hateful groups of people who are up to no good.
Even without these dark scenarios, humans have a right to privacy. Wanting privacy doesn't mean one has anything to hide.
Therefore, it's important to do everything we can to stop the collections of these masses of data. The best way to ensure that this data is not used for bad things is to make sure that it doesn't exist in the first place.