It's a trust issue. One of those companies has repeatedly broken my trust on a very important issue, the other not. I know gmail scans my message contents for

It's a trust issue. One of those companies has repeatedly broken my trust on a very important issue, the other not. I know gmail scans my message contents for contextual advertising, but it would never surprise me if facebook subsequently sold my email address to advertisers based on the content of messages, both current and historical.