When I was in high school, my best friend and I had a caustic sense of humor and would often say "nothing brings people together like hate!" This sentiment in summed up in the well-known quote - "an enemy of my enemy is my friend".
You can see many groups that are founded on hate; not all necessarily well-established groups like, well, all of North Korea or the KKK...but groups of simple friends who have nothing in common other than things that they do NOT like. Americans were united for a short time after 9/11...in their hatred for what happened. Once we started to sort things out though and we could not longer agree what to hate (Muslims or American Imperialism), it all went to Hell and we were back in our segmented groups.
A love for something quickly burns out, say, the book club I started a few years ago. Happy, content people can be pretty flaky, skipping yoga class, forgetting your quilting club. Happy, content people don't have a desire to get together with other happy, content people to talk about what makes them happy...while people often throw back a few beers and rant for hours over the same things that they hate.
Perhaps it is because happiness is more transient and varies so much from individual to individual. For example, some people are moved to tears by a sunset. Others are moved by a sunset, but only if it's wedged between two mountains, for another it's the sunset over the beach. For those who drive home from work in the Westard-ly direction - it's just a blinding pain in the ass.
Things people hate, however, are concrete: taxes, red lights, the View, the "No Spin Zone"....these things are solid, you can reach out and grab them.
"I love sunsets"...is often met by blank stares, but say "I hate traffic" and more than one person (if people are around) will chime in with their enthusiasm for hating traffic as well. They may even share an amusing anecdote. Who knows, if you hate enough of the same things, you could be soul mates!
They say blood is thicker than water, maybe so. But hate is stickier than love. People who hate together, stay together.