Exactly because money is so cheap to borrow, and the volatility that will result. The problem is the difference small moves in interest rates will make to your debt payments. It's the same problem as with oil. Oil has made small moves to the upside in the past few months, about $10/bbl. Such a move used to represent 5-10% of the price, but now it's a difference of 33-50% depending on your exact point of reference. Like penny stocks, small absolute values result in massive relative moves. This distorts markets and will cause management teams to make disastrously wrong decisions because they're being fed wrong information.

(I'm exxagerating the values here to illustrate what's going to happen)

You loan $100M at 0.25% (and like everybody, count on revolving credit) => Interest payments are 250k/year

FED decides to slightly raise interest rates (or you get downgraded, or there's a lot of other companies going broke and the banks need it, or the bond market crashes, or ... and for one of these reasons your rate goes up)

You still have $100M loaned, but now you owe $500k/year. A 100% increase in your interest expense.

And God help you if interest rates where to go anywhere near the normal minimum (4%) or their historical average (6%).

Now it is not realistic for even very good companies to borrow at 0.25%, I used that value for effect, but a more realistic value is 1.5-3% for AAA rated companies, 2.5-8% for other ratings, 6%-15% for junk rated companies. Keep in mind however that the higher ratings go up more.

So one can expect interest payments for these companies, if the FED interest rate predictions are accurate (ie. 1%-1.5% by end of this year), to jump by 33 up to 50% for AAA companies, ~70-100% for companies with other ratings and may God have mercy on junk rated companies.