What is it that makes people exclude others from something that they are enjoying? Inherent selfishness is something that comes to mind rightaway. Every human being is born selfish and over a period of time, based on their experiences and upbringing, some are just less selfish than the others, but the selfishness never goes away completely. This 'Selfishness' theory may be too simplistic a term because ultimately this trait stems from the age-old survival-of-the-fittest behaviour that our ancestors had to develop when resources were scarce.
I am sure you have had experiences, direct or indirect, of having been excluded from something you might have wanted to be a part of. Have you not come across clubs where membership costs are so high that you can't even dream of being a member? Have you not been turned away from a discotheque/club, just because you are a certain ethnicity, age, broke or just simply not cool enough? But, at some point of time in our lives, everyone has been the "excluder" rather than the "excludee". Just think of all those times when you have driven in a faster lane on the freeway and made sure that no one else from the slower lane cut in and slowed down traffic because that would essentially defeat the advantage of being in the fast lane. Pushing the argument to the extreme, would you not clothe and feed everyone as opposed to just your near and dear ones, if you were not an 'excluder'?
Niether complete exclusion nor complete inclusion will work socially. History has shown that to us over and over again. Complete exclusion benefits only the few, depriving the many and is not a sustainable social model, as we have seen from the many revolutions and wars for independence by the masses against the ruling few, around the world. Complete non-exclusion, where every one shares everything does not work as has been seen from the failure of almost each and every communist state all over the world, chiefly since there are no special rewards for the efforts of a progressive few and hence no motivation to go on since everyone gets the same returns irrespective of their efforts. The correct answer is somewhere in the middle.
As usual, I have gone off on a tangent. So I must stop now since I have work to do and mouths to feed. And until we arrive at the right answer, I will be excluding the rest of the world from my dining table and to be fair to them, I will also be excluding them from doing my work.