Yeah, Thorn Tree tends to be nothing but an ego and ethics knockdown-dragout most of the time. Thank goodness the folks around these forums are cooler than that!
Vang Vieng is just like Koh Phangan, Khao San Road, Gili Trawangan...take your pick. It's just a bastion of backpacker hedonism and debauchery -- pretty much a nonstop party. Granted, the scenery is gorgeous and there are plenty of caves, mountain biking, and outdoor things to do around there...but the primary reason to go there is to party and meet people. Nothing wrong with that, as long as you know what you're getting yourself into.
The reason people get hurt/killed is the same as at the Full Moon Party on Koh Phangan: people are trying adventure (tubing and ziplines) while shitcanned wasted drunk. Drugs are ubiquitous; you can get them on any menu. Put all these ingredients together with a lot of very young backpackers and casualties are bound to pop up.
I personally enjoyed Vang Vieng, even though I'm pretty sick of seeing the damn Tubing T-shirts everywhere that I go.
Here's an article I wrote about it last year:http://goseasia.about.com/od/laos/a/tubing_vang_vieng_laos.htm