If your normalize getting it done and exclude people who don't from opportunities, you incentivize people who want to participate, not just in receiving the benefits, but in participating in the group.
I think of it much the same way I think of driver's licenses. I believe if you are driving on your own private property you don't need one. But if you are using public roads and putting people at risk, there's an expectation of training and the ability to revoke permission if you harm others.
That largely works pretty well at keeping the pool of deniers down to the true-believers; it turns out that many anti-vaxxers give up their beliefs when it becomes personally inconvenient to hold them.