The problem with Metafilter is that $5 over time hasn't scaled. It's been $5 since they implemented it way back when, and as the popularity of the site rose, $5 wasn't enough to stop people from registering to add their pointless commentary anyway.
A few years ago I used to really find value in their community and felt that the added registration fee filtered out people that were just there to give bad advice on the green or self-post on the blue, but for the two years or so, it seems as if paying such a little amount makes people even more likely to post crap because they feel some sense of validation or privilege after payment.
Additionally (since SA was mentioned), there are so few moderators at MF that subtle trolls and misinformation loudmouths are prevalent (some have been known for their antics for several years) and threads derail and turn into a get-off-my-lawn!-fest really quickly.
A few years ago I used to really find value in their community and felt that the added registration fee filtered out people that were just there to give bad advice on the green or self-post on the blue, but for the two years or so, it seems as if paying such a little amount makes people even more likely to post crap because they feel some sense of validation or privilege after payment.
Additionally (since SA was mentioned), there are so few moderators at MF that subtle trolls and misinformation loudmouths are prevalent (some have been known for their antics for several years) and threads derail and turn into a get-off-my-lawn!-fest really quickly.