I can't fully agree with this. If that were the case then people would have been first rate a-holes during the great depression, but all reports I can find is that most people took people 'hard on their luck' in and fed them, clothed them, and if possible got them at least temporary work.
I think the main reason people are rude is because sometime between the 60's and today, having manners became elite and 'uncool.' It's much more socially acceptable to fart, drop your pants to your knees, be a judgmental asshole, and then top off the cake with a bit of snide rudeness. Two years ago I had a now former friend tell me that he felt that being nice as a matter of courtesy was not relevant in our society. There's a reason he's a 'former friend,' about the fifth time he decided to be a dick because it wasn't 'relevant to be friendly' I told him where he could shove his society and walked away.
The OP's post is why I've become a hermit. I've literally had it with people in general. It's much more mentally gratifying to stay in the house with my wife and kid, smoke some herb, and maybe once or twice a year go see my hippy friends at a drum circle. I won't go to the polls because it's a pointless activity of electing the smallest of the two biggest assholes this country could find. Unless legalization is on the ballot, the rest the world can deal with their own fricken mess. Unlike most civilization I learned to eat with silverware, hold it right, and even know what the fucked up little forks are for. I infinitely prefer to be nice to just about everyone, however the opportunity is often derailed by the people I'm trying to be nice to.
I simply won't play in the sand box anymore, it just isn't worth it.