Since when we decided it is OK to install global tracking for everybody, whether they want it or not? The User-Agent is still visible to the website I'm visitin

Since when we decided it is OK to install global tracking for everybody, whether they want it or not? The User-Agent is still visible to the website I'm visiting. It's enough that a few large websites provide stats summary for their users. It is not necessary that Google, FB and co. track the entire Internet.