The negatives are several and far-reaching: Israeli security will be further undermined by the release of someone who has vowed to kill again; justice will be undermined by the terrorist being released in spite of his crimes; and Israel will be shown to be a cooperative partner in a bad trade at best, or in its own extortion at worst, and in which Hezbollah would believe that springing additional terrorists just involves killing some more Israelis and then using them for trading stock. It's a bad deal.
There are families to consider. But they also probably perceive that this does not involve the validity of a prisoner exchange, wherein only the permanently incapacitated are traded.
This whole thing is an unfortunate comment on the thinking of the Israeli government. The Allies never would have considered trading healthy SS prisoners for the bodies of thier downed airmen, because the priority was to win.
And it shows, of course, the crude inhumanity of Hezbollah in effectively holding the grieving survivors hostage, something that most of the world is proficient at taking no notice of.