Absolutely, and not because we are such ravenous hunters, but because our species as a whole has such utter disdain for the environment. Global temperatures are on the rise, resulting is melting ice caps and desertification. Polar species are losing territory because the ice they call home is turning into open ocean. Places like California are literally drying up, which will cause loss of habitat for flora and fauna and an increase in desert area. And that's all just from burning fossil fuels and causing climate change. We are also actively destroying animal (and plant) habitats. We have lost about 20% of the Amazon Rainforest in the past 40 years due to deforestation. And what usually takes its place? Grasslands for cattle, which also raise greenhouse gases, and expanding development. So glad the only price to pay for more grassland is destroying the home of countless exotic animals.

How would humans not be to blame? They hunted them down in such large numbers that the species went extinct. If humans had not hunted them down, the species likely would not have gone extinct when it had. Where's the doubt of the cause?

http://www.mnn.com/earth-matters/animals/photos/13-animals-hunted-to-extinction/bubal-hartebeest

Loaded question.

Of course humans are responsible for extinctions.

The same holds true for other organisms, nature, cosmological events, etc.

Extinctions happen. Modern Medicine/Hygiene is responsible for the deaths of countless of micro-organisms.