Human Testing

So I was reading this article on FoxNews.com and it spurred some interesting thought.

EPA to Allow Pesticide Testing on Humans

In a typical experiment involving humans, volunteers are exposed to very low levels of a chemical, perhaps up to the point when the very first biochemical changes in the blood, or the very earliest clinical signs of the chemical (such as slight dizziness) are observed. The highest exposure level where either no significant biochemical or clinical changes are observed is then divided by 10 (an arbitrary factor used to provide a margin of safety for potentially more sensitive people in the population) to arrive at the permitted exposure level.

Now, I never really understood what was the big huff about human testing. As long as it's being watched and strigently screened, so what? Wouldn't the tests be more accurate with humans anyway?

I am a large proponent of human testing.