Biodiversity is what makes life on planet Earth possible. It is how organisms are able to thrive and function on both micro and macro levels. To take it away would be catastrophic to not only the lives of the plants and animals themselves, but to humans as well. Loss in biodiversity in any ecological system, whether it be small or large, will show up directly or indirectly and can have huge impacts on the surrounding life.
The definition of biodiversity, according to the Stanford Encyclopedia of Philosophy, is the variety of life in all forms which includes individual genes to whole species to whole ecological systems. The word itself comes from two words, biological diversity, and did not become a new term in science until 1986.
To not consider biodiversity an important aspect is to deny that humans rely on anything that is provided through plants, animals, microorganisms, geological conditions, and even specific climates. Without any of these, humans would suffer and die. After all, humans evolved to depend on biodiversity to multiply and thrive just the same as all other forms of life have.
On a genetic level, biodiversity of genes is one of the most crucial elements of life. When an organism, whether it be a bacterium or a giant sequoia tree, has a diverse genetic background of both dominant and recessive genes, it is more likely to survive and pass on these genes when it becomes mature to reproduce. An organism with a very limited genetic background caused by inbreeding or various mutations will have a reduced capacity to reach maturity since many genes needed to survive may have become damaged. When organisms are unable to reproduce, that species will cease to exist.
When a species that is thought to have no impact becomes significantly reduced or even goes extinct, the effect of its loss may not show up at first and may take years before the domino effect becomes apparent. There are too many examples of this to list. Even on the microscopic level do things quickly get out of balance such as when broad spectrum antibiotics are used which are designed to wipe out all types of bacteria and does not discriminate between harmful and harmless types. Just like on a larger level, when one species that keeps the ecosystem in check is suddenly not there any more, the organisms that are normally kept at healthy sustainable levels will suddenly have a population explosion which creates more problems for the organisms farther down the line.
Everything that lives and breathes on Earth has a specific place and role. Disturbing this balance and reducing the biodiversity, even in very subtle ways, has its own consequences for everything else. This is why biodiversity is important and should not be pushed off to the side as something that can be handled later. Without biodiversity, or even recognizing its importance, the world would be uninhabitable, even for humans.