I can't speak for Roman Catholic parishes, but for churches I have regularly attended, it's a bit of both.
It can be a bit of an echo chamber because the people there are either following and worshiping God, or at least seeking him in some way.
It can be more diverse than an echo chamber because that one message also draws in people of different backgrounds, who would otherwise not take the time to congregate together. I'm not going to go somewhere to specifically meet Democrats, for instance. But since there are Democrats who are still drawn to the Gospel, I meet them through church, and since I put Christ over politics, we actually talk.