Investing in mining can certainly be rational.
Unless the owner has such bad business sense he destroys any and all value the 'company' may ever had in one fell swoop. Like what's happening to a certain devilish little mining company right now.
I probably should have bolded the "can". Obviously, you have to make a careful evaluation of whether the person trusted with your money deserves that trust. And mining will always be risky. Generally speaking, IMO, buying bitcoins and holding them is usually better than buying mining gear and mining with it.