Today I read an "inspirational" facebook post. It was something along the lines of: A positive life is not possible with a negative mind, or some other happy sounding BS. So I'm going to lay out the reason that negative people are the not only necessary, but the reason positive people can be positive.
The negative primitive man was the one who cooked his meat, even though it was rare anyone got sick from eating raw meat. This led to basic food preparation, which led to surplus, which led to not having to follow the herds of animals. This led to the rise of society. (Obviously there are more steps)
Positive people will contentedly tell you not to make a big deal out of little problems. After all, gas lights were mostly safe. Rain will eventually fall. You can just get fresh food from the field. Except that when gas lights fail, people die. The rain sometimes waits until you die of thirst to fall. Sometimes it snows, and there is no fresh food.
Negative people see themselves, and the world, beset by problems. They invent light bulbs, desalinization methods, and canning, curing, and smoking, to preserve food. Does this make them less pleasant to be around? Absolutely, if you're a positive person. Do we make fun of positive people for failing to recognize the problems biting them in the face? Constantly.
In short, a positive outlook will keep you from recognizing a problem, and therefore keep the problem from being solved. A negative outlook sees the problem. And while not all negative people will solve problems, they see them. If you don't acknowledge a problem, you can't solve a problem.
So call us jerks, killjoys, buzzkills, whatever. But research some inventors, innovators, and visionaries. (da Vinci, Edison, Tesla, Ford, Jobs) Their contemporaries called them all manner of synonyms for "Negative". They may have envisioned a brighter future, but it was because they clearly saw the problems of their day.
If you only see the positive, you are happy with how things are. If you are happy with how things are, you aren't working to change them. Negativity innovates; Positivity stagnates. The negative thinkers may not be happy, but if "ignorance is bliss" then bliss (positivity) is ignorance. That would be the symmetric property. (http://www.mathwords.com/s/symmetric_property.htm) See how a negative person sees a problem before it manifests (like someone disagreeing) and acts to solve it?
So make room for the negative people. The world would be very worse off without us.