It should be noted that the advertisers get zero personal information, neither does Mozilla, and it has been designed in a way so that the data is impossible to fingerprint in a way that can tie it back to any individual person, machine, or specific location.
It’s a way for advertisers (and like it or not, a decent amount of the content we want has to be paid for somehow) to see how effective their ads are without anybody’s privacy being encroached on.
Should it have been turned on without informing the user? Fuck no. But there’s a lot of misinformation going around about this.
Personally I’ll still be using uBO, because I despise any ads at all, but if we are to have ads, the system Mozilla has built is just about the most ethical and privacy-respecting way to do it.