The article is a bit demagogic, because saying "we open your letters" is not the same thing as "Google algorithm reads your email."

I don't defend Google here, and I also stopped using Gmail, but not for the reasons mentioned in the article. Storing the emails and mechanically parsing them wouldn't be a problem for me, if they could ensure that those emails will not leak out of Google - but that is not technically nor legally possible (at least nowadays).