Thanks for your feedback. The reason we'are asking for people to connect using Facebook is to ensure review quality. We're currently testing some new login options. But rest assured that your data is not used for any other purpose than connecting to our system.
Kind regards, Bertrand Carton Trustpilot
UPDATE 30.12.13 I would like to inform you that we have chosen to make Facebook Connect a voluntary option. This change will be effective from January 6th 2014 for new user profiles in the UK, France, Switzerland and Germany. We believe this initiative will make Trustpilot more open and user friendly.
You can read more about our changes here: http://blog.trustpilot.com/updates-to-social-login-options/