Let's get serious for a minute here. These aren't silos or cliques and folks don't eat lunch together, happy hour together, and hang out on weekends because they clique in the same ERG. It's a way to celebrate community and gather together with purpose.
For example, the veterans ERG does a ton of disaster relief work. A lot of the veterans have unique skill sets well adapted for that kind of work. And I've seen them do awesome things. I'm thinking about joining because it seems like a good way to work in the community.
Is it about the veterans creating a clique where they can look down on everyone who didn't serve? No, clearly not. But they do great work. And they also take the time to hand out poppies on remembrance day/veterans day and host a seminar on transition of vets into the workforce, or things like that.
The value is all in the approach and what you're trying to accomplish.