The Unity desktop's search would display Amazon ads based on the query. https://en.wikipedia.org/wiki/Ubuntu#Conformity_with_European_data_privacy_law
It's like the "nazi bar" anecdote. It always starts small. You let in a bit of ads, a bit of self-promotion, then the revenue reaches a plateau. You let in a little more ads, maybe a pop-up saying that you could be more secure. Then a few years later you have a Recall situation. If you let one nazi drink at your bar, he'll bring his friends, and you'll be running a nazi bar.
I don't trust Canonical to act with integrity.