First off, to my mind the most salient aspect of the thing is that Schiavo's body ought to be hers. Her private property. Not her husband's, not her parents', not the Congress's. Hers. It should be disposed of as she wills, or, in her absence, as she willed. Now this is a liberal society, in the best sense of that word (meaning: libertarian). Liberals believe in self-ownership; it is the one thing still connecting the Left to the term "liberal". So it is not surprising to find them supporting Schiavo's "right to die", which is really her property right in herself.
It would be nice if Terri Schiavo could be consulted as to what to do with her, but that is not the case. She's not here anymore; she's dead. So the decision must be made by others. It was made by the court, as a finding of fact. Schiavo wanted to be killed in this circumstance. They may or may not be right. But to overturn that finding would be to overturn our entire judicial system. Of course, finding that she wanted to die, and giving people the right to kill themselves are different things. Suicide is illegal in many (most?) states. As a liberal, I'll fight for the right to die. But Florida evidently allows people to will themselves to be unplugged, and I am fine with that both on liberal grounds and on Federalism grounds; I don't care what they do in Florida.
Speaking of which... second thing that needs to be mentioned is how appalling it is to see the Congress trying to involve itself. Federalism, conservatives?
Third: one thing that few are mentioning is cost. Money is talked about, it being the cause of the first rift between Michael Schiavo and Terri's parents. But not the cost of keeping Schiavo alive as a vegetable. Medical care is not cheap. For the price of one Terri Schiavo meat puppet, 100 children could be kept from dying from dehydration during diarhea. Of course, by killing Terri's body we don't magically shunt money to the third world. We do, however, shunt it either to Michael Schiavo, the parents, or to insurance companies (and by extension everyone paying premiums). It helps someone. Or to put it another way: someone is paying for this.
All of that is a long way to get to saying: there are real costs involved on both sides here. It's not just a matter of "life" versus nothing. It's a matter of money, and money buys everything, including life if you're poor enough.
Some have suggested just giving the body over the parents who'd presumably take care of it. Well, see point 1. The issue of cost is more one about the motives of someone contemplating what to tell their friends and family to do with them in this sort of case. Staying alive will be taking money out of the pockets of someone, probably those you love. Do you really want to do that? For a 2% chance that I might wake up and be marginally the person I am not... well, that's worth a lot. But for a .001% chance that I'd wake up as a horribly damaged near-animal? Kill me.