I agree, but what kind of homogeneity? Linguistic diversity is a good thing, but if a group is too linguistically diverse they are quite literally incapable of communication (Barring the super good translation software that is becoming available en-masse). To steal yet another line from Heinlein, I don't enjoy snake dances, I despise crowds, and I do not let slobs tell me where to go on Sundays. I do believe a community requires some degree of homogeneity to at least start to mix together.
To me, it's some homogeneity of belief. I like the farm because it acts as a social safety net - if conversation gets difficult or awkward, you can retreat to what you know is a shared belief by everyone who's there. It keeps the connections from drying up completely. I'm not sure I get the context of the Heinlein quote though.