That sounds a lot like classic "Chinese marketing" that a lot of companies first tried when China opened up for foreign business. There are a billion people in China, so all we have to do is sign up 1% of them as paying customers and we'll be rich! Anyone can get 1% market share, right?

Of course it turns out that didn't actually work for most of the companies who tried. There has to be some kind of specific value proposition or you won't get even 1% of any market.

If only 5% of your Facebook network existed, would you use (let alone pay for) Facebook?

That conversion rate is as wishful as thinking Facebook can survive without an income. 2% would be outstanding, IMO.

I would. I like that Facebook works perfectly without messing things up. I'd pay to keep a site like that afloat.