The things that keep us apart are mostly add-ons- and people of goodwill don't need much prompting to relate to one another at the level of our basic humanity. Where it becomes trickier is with people en masse. Groups of people- communities, nations, mobs, religions, political parties- are so much stupider than individuals.
The housemates were all British citizens- chosen after they'd failed the general knowledge test administered to people seeking citizenship. Most people who take it cold do fail- around 90%. There's a version of it on the website above. I just took it and failed too. Most of my answers were guesses. Either they're asking the wrong questions, or nationality has little to do with a shared corpus of information.