So to add another reason to travel, - it's the realization how artificial borders and assumed differences between people are.
I love this reason, you're so right.
I think I'm a bit of 'all-of-the-above'. It's cliche, but I think it's always about a bit of soul-searching for me; feeding a need to discover the nuances of different cultures and lifestyles.
There's a quote that goes something like:
“I urge you to travel. As far and as much as possible. Work ridiculous shifts to save your money. Go without the latest iPhone. Throw yourself out of your comfort zone. Find out how other people live and realize that the world is a much bigger place than the town you live in. And when you come home, home may still be the same. And yes, you may go back to the same old job, but something in you will have changed. And trust me, that changes everything.”
It's a little hackneyed, but I love the last part--I really feel that when I come home from travelling.
There's probably a bit of 'fear of missing out' involved too. I wish I had the time and freedom to see every part of the world.