I took AP Environmental Sci in high school and I found it very bias, and even more so compared to the intro environ sci and atmospheric sci classes i took in college last year. maybe it was just my teacher or something but excluding the hard science we learned, everything was one sided.
with that said, i've heard this argument about the 6th mass extinction be made before. but the fact that UC Berkeley used mammals to gauge the entire world's biodiversity is awkward to me. mammals reproduce slowly, mature slowly, and live longer, so just because there are less mammals species doesn't mean the earth is less diverse. the biggest threat to biodiversity are around all the major forests in the world, deforestation is running rampant in countries that have no policy on that. hopefully they come to their sense before its too late