FWIW - and pardon the TSA comparison. But having a log-in requirement or 180/180 requirement to me is a bit of "security theater". Neither will prevent bloggers or company reps from accessing the forum because they're already enabled. Or, as CMK said, it's like "closing the barn door after the horse has already left."
While I was supportive of a log-in feature back in 2010 & even in 2012, I've changed my mind (and I was the deciding vote back in 2012 keeping it open to all/no log-in required when this went to a motion/vote the last time) & don't think it's in the best interests of FT.
FT is about sharing information freely, not trying to keep it only for a few. There's no 'stealing' a mistake fare. And it shouldn't be about well we want to get it for us/not share it w/ others.
Yes, mistake fares still occur but airlines have gotten much savvier about them/catching them w/ their own internal software &/or may not honor them. It comes down to you win some, you lose some! (you being generic you/FTers). As others have said & the mantra has always been for years. If you see a good deal, book it then as it might not last very long. That was true even pre-bloggers.
Also, FT is not the only source for mistake fares being posted (blogs, facebook posts, websites other than FT, heck, even news media, come to mind). It's the internet. There aren't any secrets anymore.
Cheers.