What is the practical, measurable impact on my life of big corpo knowing my info?

Just off the top of my head: spam, scam calls, phishing emails, credit agency hacks, every data aggregator in the world having a psychological profile on you, malicious actors who want your money having access to enough information to have a chance at getting access to your bank account. But at least advertisements will more likely be things you want.

Oh and don't forget it's not just big corpo, it's also several nations spying on you. Sure you might not be doing anything wrong now, but take it from a political refugee: if they ever want to control you, all they need to do is criminalize something you did in the past and then they already have all the evidence they need. Isn't "justice" fun?

If Big Corpo wants your data, they will get it.

That's a very silly assumption to make. Just because they have better data aggregation abilities than your average person doesn't mean they're omnipotent.

They are better at getting it than we are at hiding it.

This really sounds luke you're devolving into an All Or Nothing stance. Just because my online presence necessarily leaves a data footprint doesn't mean I should just give up and let them have everything they want.

The only solution is legislative, not individual nerds putting up knee high fences and feeling morally superior about it.

Excuse you, mine's a chest high wall.

Ignoring the assumption that legislation would ever act against the will of capital... As we've seen with the Right to Repair movement: societal change stems from the sustained pressure applied by groups of dedicated individuals. Legislation doesn't just pop into congress because one of the representatives was visited the night before by the three ghosts of privacy past, present and future in the middle of the night; it comes from representatives that either belonged to the movements or were successfully lobbied by them.

Also if someone suggesting you should care about your own privacy and/or well-being feels like an attack against your morals, you should start asking why and who taught you to feel that way about it. I don't feel like a better person than you, I feel a lot less paranoid and stressed all the time and I would wish that for everyone