I'll just quickly explain that
It used to be that the forums were pretty much private, you had to join to read anything. That was fine when the channel 4 forums first closed, as hundreds migrated over to here and TRF, and forums were still popular.
However, not being able to read forums is a massive negative on SEO and also attracting new members. It's hard enough these days to keep people posting, let alone getting someone to join when they can't see what they are joining, so the decision was made to open the forum up so non members could read and hopefully join.
It was discussed to have a private forum that only members, or members with a certain post count or length of membership, could access, but it was decided that all that would do would be create a clique of members that others would feel excluded from. Considering thats been mentioned more than once on here, we thought it best not to do that.
Hope that helps explain it