It's not just email address, I listed all required data for token sale sign up, none of them are optional. The required personal details are marked with an asterisk, they are:

• Country of residence
• Contact Email
• Full Name
• Postal Address

They specified that they will share data with advertisers and affiliates, current or future, and also upon government request, in addition to legal demand be it legislative or regulatory.

It's a matter of user discretion, I chose non participation, and thought I would share my reasons here. To each their own.