yes, that is a concern, but only for those who are investing. Not for society in general imho. The investment would lose money if it wasn't wise, and the investor who did it suffers the loss. unless, of course, this loss is subsidized by taxpayers (e.g., a bailout).

Cheaper capital allows for investments that otherwise would not have happened to happen. An example is the massive amounts of dark fiber left over from the dot-com boom. the losses from building out those fiber is suffered by the investors, but the benefit is now being reaped by whoever that purchased it on discount after the bust.

I wish the same could've been said for fracking shale oil - unfortunately, that didn't happen (and thus led to high prices of oil today). So it's not always the case that unwise investments turn out to be useful in the future, but you can't really know ahead of time.