[Lost_BiomedE]

"But it doesn't get truly dangerous until people are buying stocks with borrowed money. "

Currently, the borrowed money is nearly free money via low interest rates. A lot of games are being played to juice out every cent that can be made on being able to get cheap money. When the value of assets used to play these games are ignored vs. the diminishing profit. It becomes musical chairs.

I doubt we get your everyday Joe betting on margin like the dotcom bubble, but we have the same effect, just different users.