Well...

1. Target once used small amounts of shopping data to accurately predict women were pregnant before they themselves knew.

2. A Nebraska PD got data from Facebook to prove a woman had an abortion recently and prosecuted her.

3. you don't know what will become illegal

So, even small amounts of data can predict lots of things about your life. The government has a track record of using that data to prosecute you. And you cannot trust the Government will always align with your morals (assuming it even does right now).

And that doesn't even consider other entities & organizations in the world.

What if an insurance company wants uses public data about you to deny you coverage? What if someone is searching for people in the area with ideal houses to rob and you're on vacation? What if they use a deepfake of a loved one to scam you? Steal your identity and ruin your credit? What if they make and sell deepfake porn made of you or a loved one? What if they create meticulously engineered political psyop campaigns hand-tailored to exploit your psychology? What if this list of "what ifs" could go on nearly forever, and some "what ifs" aren't even things we're capable of knowing about?

Because that last one is absolutely true, all the rest of those are true for someone, and at least one of them is probably true for you already.

Ok, but what if you don't care?...well someone else in your life does. And even if they have impeccable data privacy habits, if enough of their friends and family don't, then they're just a single missing puzzle piece, and everyone can still see their shape.

Not to mention, you contribute to a pool of data that's used to perform these kinds of analyses on society at large, meaning you contribute in some part to each and every instance of malicious data use towards anyone, anywhere.

Is that a good enough reason to care?