I do not believe we can survive on "green goo," therefore it is very important to maintain biodiversity. This question reminds me of the old sci-fi movie titled, Soylent Green. For those not familiar with the film I highly recommend it because it highly relates to this question. Biodiversity is important.
Mankind should keep biodiversity going in order to best benefit mankind. People can not survive on green goo alone. People need to treat the environment with care and help generations to come to enjoy nature. Green goo is an unknown that could be harmful to the population and could be harmful for plant life.
Mankind should keep biodiversity because it is what makes each species different from each other. In turn, this provides each organism a role to play on the earth fostering a more productive ecosystem that encompasses a wide variety of living things. Biodiversity is also great for the production of farms because the greater amount of species and diversity there is, the greater variety of crops we have to eat.
No, mankind should not survive on green goo, because biodiversity is very important to society. Biodiversity is what makes the world beautiful. The world is full of mountains and plants and animals. We never know which part of biodiversity might be very important to us later on for scientific purposes.
Whenever people speak of biodiversity it becomes clear to me that they don't really understand the concept, let alone why they even believe that biodiversity is important. Arguing that every species should be saved, or that some arbitrary number of species decided 50 years ago is the 'right' number makes little sense.