And how did memes make that harder

Memes don't necessarily make it harder. However, memes can be used to simultaneously include and exclude -- as references to something the "tribe" gets, but others outside the tribe do not. Inside jokes are an example of such references.

When you make hyperspecialized memes, and you have many of them, you're basically fragmenting a larger pool of shared meaning into many smaller ones.

Diversity, and of itself, is not inherently a virtue -- although lots of people would like it to be. Rather, diversity in the ecological sense, leads to more resiliency. There's still have to be some kind of unifying aspect (such as, unifying on humanity as a whole, or better yet, the whole earth as a whole) within which there is diversity. There's a sense of belonging to something greater than you while simultaneously participating and relating from the uniqueness of an individual.