I absolutely love this thread. I have read some of the best answers, and some awesome points have been made, by believers and skeptics alike.
Here is my take on the whole thing.
There is way more than just one question being asked here, but I will go with 2 of them. One is "What is the meaning or purpose of mankinds existence as a whole?" and the other is "What is the meaning of my individual life?"
I personally do not think there is a purpose to mankind's existence as a whole. At least, no more so than every other living being on this planet. I do not believe that every other living creature on this planet was put here by god to somehow benefit humans, either, so in my opinion we are equal. There is no meaning to existence, we just exist.
As far as an individual's meaning of their life, that is a whole other ball game that will never have a uniform answer. Some believe there is no meaning to their particular life. They think that had they not been born, the rest of existence would have gone on just fine without them. Some believe that everyone's life has a specific role, and the rest of existence could not be without each living being. They think that existence as a whole is a huge mechanical machine, and each life is a very important cog that keeps the entire thing working. Each of these opinions has great emotional benefit to the individual. It takes responsibility off of some, and gives credit to others.
Personally, I don't feel the need to ask why. The way my brain works is how. I like to know what happened to cause life to exist instead of why. I don't believe there is always a why. I am here, and I exist, and it will never matter if I know why or not.
As far as someone comparing life having no purpose to sociopaths, well as logical as the poster made it sound, that is not how it works in my mind. Sociopaths are an anomaly, and their thinking goes against most other living creatures' survival instincts. Living creatures have had to learn to think of the greater good of their species, or their pack, or their family, or their civilizations to continue to exist. Emotions like love, empathy, compassion, and sympathy are tools for humans (and maybe animals) to use to promote reciprocal beneficial acts from others, and to continue to be a working cog in the machine that is life.
IMO. Of course.