Each user adds “value” to your site but every user adds different amounts of value. Some users (trolls, spammers etc.) even add negative value. If we plotted out a histogram of value, what would it look like? The shape of this histogram has implications for the buildup strategy.

It should be a long tail distribution of some kind but what’s the specifics of the shape? More specifically, should we focus on eyeballs or community? If top participants are many thousands of times more valuable than average, then you can get away with exclusivity, snubbing and user hostile interactions.If the bulk of your value comes from the tail, then you want to be promiscuous and accepting.

If the ends of the tail carry significant negative value (trolls and spammers can do disproportionate amounts of damage to a community) then you need to worry about heavy duty screening mechanisms. If not, then you don’t.

Is there any way to measure this? Automatically?

Complicating things is that each user does not contribute independant value. Some of the value of low quality contributers comes from their ability to make a site more enticing for high value contributors.

In the end, it boils down to: Are user hostile interactions ever useful? if so, when?