This is not a static site, it takes various kinds of user input. SSL would hide which pages you visited, which items you upvoted, and which items you helped confirm or refute.
In some countries, this kind of information could be a powerful tool of repression. The police knocks on your door and asks "You helped confirm Rumor X about our Dear Leader. Tell us everything you know about Rumor X!" (Of course such countries also tend to block domains like grasswire.com, but some might choose to keep it unblocked for a while and use it as a honeypot to pinpoint dissidents.)
The multimedia-heavy, AJAX-heavy interface also makes it a royal PITA to use the site over something like Tor.
We will absolutely be doing that. Having lived in China and eastern Ukraine the need for anonymity is very real, and very important to us. Thank you for the suggestion.