> Not 100% sure how I feel about random companies being able to definitively identify me.

But that is not what we are talking about. It is not that you are browsing the web randomly and some random company identifies you as d1sxeyes.

It is that you can identify yourself towards any company if you choose to. Then you can decide if that is in your best interest or not.

It also is not necessarily your actual ID. As far as the individual website needs to know, it could just be a random string of numbers and letters. As long as it's the same string each time they ask the authentication authority to confirm you.