In fact it did NOT prompt me when enabling analytics, but it did display a notice (hidden in several hundred lines of output during brew upgrade):
-------------------
+ 5a9e19f...7f13b37 master -> origin/master (forced update)
* [new tag] 0.1 -> 0.1 HEAD is now at 7f13b37 Merge pull request #1562 from woodruffw/check-admin-group
==> Homebrew has enabled anonymous aggregate user behaviour analytics
Read the analytics documentation (and how to opt-out) here: https://git.io/brew-analytics
==> Tapping homebrew/core
Cloning into '/usr/local/Library/Taps/homebrew/homebrew-core'...
remote: Counting objects: 3765, done.
remote: Compressing objects: 100% (3654/3654), done.
-------------------
I do not consider this a prominent warning. Rather it is sneaking analytics silently in the back door.
Looking at the website one of homebrew's developers (or at least the website developers) is based over here in Europe. He might be a nice target if you want to raise a stink and litigate. If I'd were a contributor I'd not want to have my name associated to something like this, even if it just happened out of stupidity not out of malice.