He wouldn't need to buy all of them. If his purchasing streak pushes prices up so high, or so fast, that nobody will sell them or use them, then for all practical purposes, bitcoin is dead. A currency with no current is not.
Of course. It is so easy.... er wait no it isn't.
Rising prices will cause people to NEVER (till the heat death of the universe) sell or trade.
Is that your claim? Really? Can't find any flaws in it?