I think what the kid did was wrong without a doubt, if he was going to put the cat down there are more humane ways to do so. The thing is there are evil children all around the world who tend to get misguided ideas on how to spend their time, and this child in the video is probably not a specialty of Greece.
I also agree with John, that there are more important issues like abortion that one could be concerning themselves with..and clearly no matter how you look at it, a worthy human life is infinitely more valuable than a cat's. Again, this doesn't make the kid's action acceptable at all- I'm aggreeing with another way of looking at the whole situation that is perfectly valid.
While addmittedly it's not a good idea to want to boycot tourism to Crete and Greece, I think you're right in that something needs to happen here. There is no benefit to the tourism industry to have sick and mistreated animals not being cared for .. where visitors would see this happening and their own country's methods of handling animals differs significantly they're surely going to notice and talk negatively about it.. and this could be even eventually be to the peril of those who don't care too much.