Earlier quoted context omitted.
The value of a stock is the total future profit of a company priced in today's dollars.
So if I'm understanding correctly, if they only make $1 per user per year, and do that for the next 166 years (not adjusting for inflation,) then they're just as well off?
I would say the probability Facebook is making much in PV terms 166 years in the future is very low. Facebook has such a high value now because they have lock-in for their users; a user has a lot of Facebook friends and so can't make a unilateral decision to leave the platform and still have access to the value having their friends on the platform provides - and so that limits the threat to Facebook right now from competitors. However, there are still significant threats to Facebook longer term, and some of those threats could open Facebook up to threats from other firms with smaller costs that Facebook can't easily transition to compete with profitably long term.
Facebook therefore has very good prospects short term, but this position is still relatively precarious and the probability of maintaining as many users and as much revenue decreases progressively into the future - the probability of high revenues continuing after 50 years or even 20 is so low that it is not worth taking it into account when working out the intrinsic value of a share, and profits in the near future make up a much greater proportion of the total 'area under the integral' (i.e. future profits).
Formally: v = -E(L_{total}) = integral_0^infinity (integral_(-infinity)^infinity (l * P(L(t)=l)) dl) dt where v is the intrinsic value of a stock, E(L_{total}) is the expected total loss of a stock in Present Value terms, and l and t are bound variables used for time and rate of loss, L(t) is a random variable representing rate of loss at time t, and P(L(t)=l) represents the probability that the rate of loss at time t is l.