There are two challenges which combine into one problem:
1) The amount of bad content posted to a forum rises exponentially with the size of the membership. For every x new people reading, x^y bad content is posted. This is because a large target becomes much more attractive to spammers, trolls, and anyone else looking for a cheap audience.
2) It is extremely difficult to find good moderators. A good moderator will be, within reason, consistent, reliable, AND unbiased. Even with a salary at stake, it is difficult to find people who are even two of those things.
In order to succeed in moderating content well, you need to leverage reliable moderators (today, this means rare humans) with unreliable ones (text analysis and less rare humans) through some sort of statistical system. To date, we have not found a reliable system which can work at scale with this problem, but my faith is in a transparent and verifiable web of trust type system. Slashdot does pretty well, but it's still too opaque, in my opinion.
There is nothing wrong with automatic flagging, only with automatic action after that flagging.
And key here is, a way to legitimately dispute.
Your case is not a parallel case.