I don't think it goes quite that far, but you certainly have to question the motivations of businesses who offer free services as well as any company that derives a significant chunk of their revenues from advertising.

That being said, you can always encrypt your email if you are concerned about your privacy. A starting point would be to use HTTPS for webmail or one of the encryption schemes for POP3/IMAP. It won't accomplish anything with respect to your email provider, but it does prevent your internet service provider from snooping. Encrypting the messages themselves is also an option, and offers much better protection. Alas, the requires cooperation from those sending you email and those receiving your email.