I would put it into three categories:
1. Safety
Bad privacy opens you up to several crimes, e.g.:
- Identity Theft
- Spear Phishing
- Doxxing
- https://github.com/tenacityteam/tenacity/issues/99
Yes, in an ideal world, the criminals wouldn't do these crimes and telling people to heed their privacy for this is borderline victim-blaming, but our legal systems still seem completely overwhelmed with the reality that is the internet.
2. Psychological Warfare
Advertisements have long gone past their initial purpose of informing customers, so that they can make better decisions.
They actively try to get customers to make worse decisions, i.e. buying overpriced articles and buying articles that they wouldn't otherwise buy.
Really, an advertisement that informs you of the most cost-effective product for something that you would have bought anyways, is a horrible advertisement.
And one way to make ads less effective, is to not give them personal data.
This is also particularly important with political ads, where you may be communicated a wholly different message than your neighbor.
And speaking of politics,
3. Right to Democracy
Democracy doesn't come for free. Every so often, it needs to be defended with protests.
And as such comes the question: Would you feel comfortable organizing or participating in a protest?
Would you also still, if an extremist party in your country came to power?
Ultimately, it's a deed of every citizen in a democracy to be able to defend it. And for that, you need privacy.