Following the links on Wikipedia I got to this article: http://www.aafp.org/afp/991115ap/2269.html It lists low fluid intake (as well as restricted access to a bathroom) as a risk factor in kidney stone formation. However, another article (http://www.ncbi.nlm.nih.gov/pubmed/12576800) reports some conflicting results. Apparently, as people drink more water, they consume more sodium to compensate, negating some of the benefits.
I wonder what someone who actually knows about this would say. Also, 2L isn't that much, but I wonder if I drink 8 glasses of water a day. An experiment is in order.
Toxins? Again, no specific answer, but the food is not necessarily "clean", so that's what our kidneys and liver are for.
Obviously, I can't speak for any large body of humans without some kind of rigorous scientific evidence, but passive observation of coworkers, friends, and family leads me to believe that most people don't drink nearly enough water. It could be different where you live though.
By the way, I mentioned specifically too much water. You only need to drink when you're thirsty. I'm asking what benefit you get from drinking water when you're not thirsty.
By the way, "people are dehydrated a large majority of the time" -- citation needed.