The business cycle always replaces one burst balloon with another in different forms. Presently, the biggest balloon ever is the US treasuries. After the tech bubble, it was replaced with a mortgage bubble plus a commodity bubble(oil, steel,cement,food)
The government is printing money and sooner or later nobody is going to be buying. The downside is limited and upside is inevitable to anyone willing to hold long enough. Interest rate will eventually go up, with inflationary pressure down the line.