The problem is, everyone buying now is buying because they think more will buy after them and drive the market higher. At this rate the time will soon come when the "150 million" accounts are open and everyone is in the market, all that's left to inscrease share prices are profits/dividends, and everyone will realize that then their returns will be lower than 1% because you've paid 100 for a company that generates less than 1 in profits, which will lead to the exact opposite of what is happening now. Bottom line is that the go up 400% go down 80% is net negative, which is why the government is airing cautionary alerts on public television...
Sure it can go another 2, 3, 4 thousand points higher, it doesn't matter, all that matters is where fair value is, because that's where it will go back to. You don't know where the top will be but if this is it then fair value is already far away enough to make the drop very scary