<< I think the low probability dystopian possibilities are severe enough to outweigh the casual benefits. >>

I agree, although perhaps I am hypocritical, because I use gmail and google maps. I have jettisoned FB though.

<<Things have already been leaked, and what has the material damage been?>>

I think you're probably right, that this was their main point. To address it, I'll just briefly point to

(Edit: I may not have directly addressed their point here, but I dont think personally that I need to actually see something bad happen on US soil to assume it can't or won't happen if there is no principle to prevent it)

- the myriad oppressive regimes and violent drug cartels that use even publicly-available information to target political opponents.

- the ability of even casual users to create advertisements targeting (or excluding) ever-smaller circles of identifiable traits

- vast and secret subpoena powers by the US government and her allies

- severe political polarization centered on the US, in which the government and its powers flip poles every few years: what is okay for "our guy" to do (e.g. secret assassination lists, secret trials, rendition) will be available for "their guy" in a short while.

- AI being to identify ever-accurate and surprising correlations between lifestyle choices and political views.

Hopefully, nothing bad will happen.