It doesn't matter how you dress it up or with what extenuating circumstances you cite to rationalize it, agreeing to pay what amounts to a 500% rate of return is insanity. Depending on a single large investment that had to have been known to be, at the very least, high risk, to make said contract profitable is even further insanity.
And to rub more salt in it, the Mets had a golden opportunity to make this contract go away by declaring bankruptcy when they had the chance, blow up the whole thing and start over from scratch. Instead, they decided to keep a tenuous situation afloat by borrowing money.
Of course, if they were actually a good team, all of this may be forgivable, but there they are, sitting at the bottom of the NL East and not making any significant moves to try to better themselves. For a team in one of the biggest money markets in the country, that's pathetic.