What people think of these programs is often linked to the perception of the product being sold. If a cigarette company did this, people would be pissed. McDonalds is kind of an edge case - everyone knows it's not great for you, but it's not as harmful as cigarettes or drinking so you get mixed takes.

The classic case here is Target inferring that someone was pregnant before her family did[1] - so yeah, this is nothing new.

[1] https://www.forbes.com/sites/kashmirhill/2012/02/16/how-targ...

Where it gets "you really should care about this" are things like your insurance carrier using this sort of data (which is for sale to all comers) to, say, increase your premiums under the guise of "your 2 Big Mac a week habit makes you a bigger risk".

Altria already does this to some extent. See their Digital Trade Program.