The whole thing's alittle sketchy on the details. Going by this:
In his defence, the artist has claimed that what he was attempting to prove was that those who saw the suffering of the dog just walked on by and that if it had been left on the street to die, no-one would have even known of its existence.
It has also been reported that the dog did not die but escaped, and that it had been fed by Vargas and was only tied up during the gallery opening times. It has not been possible to confirm this.
I can not necessarily justify his actions, nor call them art, but can see how the act might, by alerting people to what happened right in front of these visitors to the art gallery, change people's perceptions about the world around them.
Perhaps you live in a "nice" neighborhood, in a "nice" town, but right now, there's millions of living beings dying from the same sort of neglect, due mainly to humanity's complete and total fuckwit stewardship of a perfectly lovely planet. God gave us this paradise, and we've turned it to a shitheap in record time.
What I'm trying to say here is: You can cluck your tongue and say, "How rude!" about this act(about which the details seem sketchy at best), or you can peel the blinders off and look at the big picture. There's people, tens, hundreds-of-thousands of them, dying like dogs in Darfur, with the whole world watching...and no one is coming to save them. That's just one hotspot, and we're talking strictly people here. Death ain't taking no holiday in the here and now, people. Death is working overtime, and business is booming.
So stop. And ask yourself, deep down, what's really important during your time here. I think that's what the guy is trying to get across, in admittedly blunt terms, in his "exhibit".