I use google chrome with adblock and adblock plus installed, 2 free ad-ons that remove most web ads. So my facebook page has no advertising on it. Well apart from a few companies I subscribe to.
Now how many other tech savvy people also block web advertising? 10%, 20%...50% so at an extreme now from your 1 billion users you now only have 500 Million that see ads. Now you need to make $200 per user, seems far fetched to me.
