Is Google justified in using the search history of unaware customers to target them with ads?

Please review blog post: 
https://adexchanger.com/ad-exchange-news/first-google-lets-advertisers-use-search-data-youtube-ad-targeting/
Answer the following question:
Is Google justified in using the search history of unaware customers to target them with ads?  Take a stance and support your answers with actual examples. 

Please include references