The thing is, it probably won't affect your life. There's millions of people willingly giving up their information to the internet, and it's not like every single one of them, or even a majority, will face any consequences.
But what if you suddenly decided to change the world and become a politician? Well, I sure hope you never directly googled for some particular genre of pornography, specially if it's something that's widely frowned upon.
And that's just one example. The thing is, if Google, Facebook, etc. ever want something from you, they probably have the power to destroy your life if you don't give it to them.
Do you really trust each and every tech company with access to your data that they won't ever use it to cause you some sort of harm?
And what about governments? No, I am not talking about your fancy democratic government, I'm sure others will point out what's wrong with that assumption. I'm talking about those "russian hackers" the USA is so confused about.
Chances are, google knows enough about you to piece together who you're likely to vote for. What if they start targetting you with ads meant to mobilize voters, because they know you're likely to vote the "right" party? Or what if they bombard you with stories about how democracy is broken anyway, and elections are manipulated, because they think you might vote for the "wrong" party?
"But google would never do that" I hear you say... "And if they did, I wouldn't fall for it"
If you knew about it you wouldn't, but you wouldn't know. These things do work, otherwise google wouldn't be so filthy rich with their dozens of products that they run at a deficit for years. Ads work. Online manipulation works.
What does that have to do with the "russian hackers" I mentioned above? Well, what do hackers usually do? Right, they hack. What if google gets hacked? Suddenly another nations government has access to millions of (insert your country)s citizens to manipulate.
"But google won't get hacked, and neither would facebook"
Sure, I won't hack either of them and neither will you. But we're not the Chinese government, with as much money to throw at a room of programmers as it takes for them to make it happen.
And what about third party contractors? They may not have the same security standards or resources to protect your data.
I could go on and on about this, but I'll leave that for others.
In conclusion: Privacy does matter maybe in the same way climate change does. It's not like driving your car for an hour will make it one degree hotter all of a sudden. It's a complex process that nobody fully understands and that's very hard to grasp, yet everybody who spends time researching the subject certainly agrees that there is great importance in it and it does affect all of humanity on a scale beyond what we see in our day to day lives.
EDIT:
Why did I even bother writing all of that? Just read [this](https://en.wikipedia.org/wiki/Stasi) and you should get an idea of why you should value complete and unconditional privacy.