That's true. The obvious tradeoff is that nobody wants to add friction to account creation, especially when they're first starting out and don't have network e

That's true. The obvious tradeoff is that nobody wants to add friction to account creation, especially when they're first starting out and don't have network effects, and abuse detection is tomorrow's problem. And then if you try to add it afterwards when you've gotten popular you'll be deafened by the screams of everyone who's gotten used to a free experience. Plus, your support load goes way up because all your users are now paying customers. I've heard that it worked for Metafilter but I wouldn't be surprised if it prevents a site from scaling users past a certain point. (I mean, sounds great to me, but probably isn't what someone running something like Reddit wants.)