Why do we need to have a blanket rule for this? What does that rule do that simply looking at posts and saying "okay, this is relevant and can stay" or "this is derailing and can be deleted" cannot do?
I would say the blanket rule came into effect recently because we have had a lot of peanut gallery...ing, in the recent complaints, nearly every one in the last couple of months have exploded into a multi-page shitstorm; the rule is severe, but a loud proportion of the community has shown that they can't be trusted otherwise.
The rule in and of itself is not bad, it's just the other hand, in an ideal world, it would work fine, everything would be worked out in an unbiased fashion.
Real life isn't ideal however, a better suggestion than removing the rule, however, may be to alter it to allow evidence from other people to be presented, and strict penalties for shit-posting and flame-inciting in those threads.