The options for CJ at the deadline had been reported as Gallinari+filler+pick from Atlanta, Powell+Kleber/(maybe Hardaway?)+distant first from Dallas and the New Orleans deal. I can absolutely guarantee that this board would have been going bezerk if we had kept CJ past the deadline, and the same posters blasting Cronin now would be blasting him if he had turned down all offers and hadn't made a move.
Cronin likely took a gamble that the pick would convey this year (and as of the time of this post, of course, it still might). If it doesn't convey, is it not still a gamble worth taking at the time? The Milwaukee future pick may not be as shiny of an asset, but it still is an asset that can be utilized. Hell, that pick might be used to acquire Grant anyway (so really there would be no major difference on our end).
We can argue that Cronin should have negotiated for better terms after this season, but what if NOP simply says no. New Orleans was certainly interested in CJ, but I've never gotten the impression that they HAD to have him. NOP could have easily said, "meh, if you like those other deals better, we're fine." I'd still prefer Hart, the Milwaukee pick, and additional cap flexibility (along with the seconds, etc.) to the other offers.