> Can anyone explain to me how this could be used against someone? I'm asking completely seriously as I don't see any harm in this no matter how hard I try.

This is called the "nothing to hide" argument. If you currently have no foes and are generally closer to the elite of a society than to the margins, then these few little data points collected on you (pseudo-anonymously or not) cannot really hurt your.

But as your digital shadow grows (and with google analytics et al being used to extensively, it certainly is) and you drift to the margins of society, possibly developing some foes in the elites in the process, the information about you that is now available to people in power becomes more threatening for you.

Say, you're now a black, female, delivery driver in Detroit instead of a Silicon Valley software engineer. Once you give cause for scrutiny, say, a conflict with your employer, the digital shadow of data-points can be searched to find anything that, taken out of context or not, can be used against you.

Or, put differently in famous exaggeration by Cardinal Richelieu:

  If you give me six lines written by the hand of the most honest of men, I will find something in them which will hang him.