Most browsers now will automatically flag any website that is lacking an SSL certificate. If a website starts HTTP vs HTTPS it is lacking this security protocol. Think of the information you send on the internet as a transaction. Http would be like using cash - there is less security with it, easier to be stolen or intercepted, etc. Https is like a credit card, with additional layers of security and protection.
The only thing that https would really protect on this website is your password. That is the only "encrypted" item a hacker can gain from the forum that is useful, unless I suppose you are sharing information in private messages like credit card numbers, etc. A forum isn't usually the target of a hacker anyways because they know this, too. There simply isn't enough reward for the trouble.
Basically don't use the same password here as you do other places.
SSL is also an additional yearly cost.
