Obviously, the capability of humans to think, reason and create give us an indisputable advantage over other species. But that doesn't mean that human life is always filled with love, creativity and growth. As Nikhil pointed out in his original essay, many individuals are born, go to school, get a job, get a spouse, watch TV in the evenings, give birth, go on bi-annual family vacations, retire, get severely ill and die. This highlights the mundane nature of human life and why it is hard to argue that human life is precious or worth making 50,000 species go extinct over.
It is true that individual humans can live meaningful and rewarding lives, but on the whole, it is important to recognize the dullness of many lives which can be attributed to our increased access to technology and resources. That's not to say that human life is not valuable - far from it. Human life does hold a unique value when compared to other species - but that doesn't mean that we should ignore the other effects or consequences of human life such as the extinction of other species or the depletion of resources.
At the end of the day, while human life is certainly valuable, it's important to acknowledge and consider the consequences of our actions. That doesn't mean we have to give up all hope; it just means that it's wrong to assume that all human life is equal in value. Every individual has the power and capability to make positive changes in the world, and that's something that is definitely worth protecting. After all, don't you think it'd be a real shame for us to drive 50,000 species extinct only to realize that our lives weren't even as precious as we thought?