Life exists on this planet in different shapes, sizes and forms, so much that it may be difficult to understand why so many different forms are needed. For example, when I was a child, I never understood why those tiny bacteria, viruses had to exist, when all they do is just make us sick. They are so small that they are not even visible with naked eyes.
They exist because they all have a role to play. Yes, some bacterias make us sick. But there are other bacterias who save our lives, those who perform many of our essential bodily functions such as digestion, neutralize toxins. Bacterias help decompose dead bodies. Without bacteria, all the millions of dead bodies from the wars or bubonic plague would still be piling up all around us. Bacterias decomposed the bodies, putting an end to the epidemic, returning the nutrients they consumed from nature back to nature for us to consume now. They act as agents of the greatest recycling project of our nature. So the answer to my question is, if they never existed at all, we would have never existed. We exist because they exist.
This is true for every single organism in some way or the other. Some directly, some indirectly. We cannot live alone. Humans are social animals, remember!! Let's now expand the definition of 'social' beyond humans, if not for the sake of them, then for the sake of our own survival.