Regarding multiple accounts:
These are, with some exceptions, against the rules. People who make fake second accounts are usually dishonest or trolling – and that’s not something we want a part of our community.
Regarding the forum being open:
All this means is that people don’t have to register to be able to browse and read the topics. Even if the forum did require registration, it really isn’t a lot of effort to go through. Unless we block registrations completely, but in that scenario no one would be on the forum in the first place. Keep in mind that this forum isn’t being broadcast to some public space. People have to find it themselves. I detailed it a while ago here: Content Guidelines - #11 by Robin, but the conclusion is this:
There’s a 0.0000000001% chance that someone you know will find you on here
and a 0% chance if you are careful with what you post.