Superficial (but still valuable) exposure to other species and cultures through semi-casual RP, is what I'd call playing alternative races in DnD.I find it difficult to believe that most people find it easy to understand what other people whom they are close to - their friends, families, and lovers, truly think. Let alone those people who have opinions that are truly different. Let alone those who come from different cultures.
if you know what it is like to walk in the shoes of all humanity, you are a better person than I will ever be.
IME, many people who play non-humans are exploring stereotypes that they would be embarrassed to ascribe to a human.
I do not think playing Warforged is going to provide insight comparable to truly understanding other real people, but RP is quite literally trying to put yourself in other people's shoes, even if it's one "ok" character at a time. Even if it's superficial, playing a non-human is still a different experience than being a Human character- gameplay (a more than sufficient reason) and otherwise, if you care about RP (which has equal merit). You get out as much quality as effort you put in, and that principle is proof enough that there's merit to having the options we have, even if they're "weird." Same goes for classes, settings, specific ideas, etc. Anything can be a great, fully worth it idea/implementation.
I'm playing a pretty stereotypical Elf Wizard right now, but I feel like I'm thinking about more facets of the character's life in the world than if I played Human. Simple stuff, like what does he do with the free time Trance gives? How will he react to the party being magically put to sleep around him? What led to him being who he is, in more detail? Hey, a Gith I've got coming up has me thinking about the race's lore. There's stuff that isn't best achieved through Human.