If, suddenly, one billion people couldn't use Facebook anymore, then it would be because of a literal apocalypse. Facebook can't just disappear overnight.
You lack imagination, if the great firewall of China decides to block Facebook, poof, one billion less users. Overnight.
That is, if it's not already blocking it, probably is, thinking about it...
North Korea is virtually disconnected from the rest of the world, and there's nothing we can do about it (except maybe start a war?). No innovative cryptocoin with the most powerful proof of algorithm and the fairest distribution of them all will be able to reach them.
Also, Bitcoin is different in that, while Facebook severs can be shut down tomorrow (but highly unlikely), it's literally impossible to just shut down Bitcoin servers without bringing down the whole Internet in the process.
I argue that allowing the block size to grow is equivalent to making Bitcoin as vulnerable as Facebook currently is. In other words, centralized enough that it becomes vulnerable.
Then you should know by now why your argument is wrong. Read all the discussion that has been happening in this thread.