One thing might be worth mentioning. To most religions, helping others is one of their shared core values. This means that everyone joining a church can expect (even on a rational level) that he recieves a warm welcome. As the communities themselves also feel they ought to be warm to newcomers, that is what usually happends too.
The problem rationalists are facing is that the community is essentially dog eat dog where everyone tries their best to scrutinize others thoughts (as this is the “rational” thing to do) and then to bash the hell out of them for every small detail missed because “this is critical for becoming more rational”.. although more often than not it can probably be ascribed to just that person wanting to show that he is smarter and a “better rationalist”. And people fear this criticism, even when it might not materialize. They know that in order to be accepted, they need to be really rational. This sets rather high standards on self confidence for joining.
What religious groups have over us is that for them the competition to be a better christian/muslim/jew doesnt interfere but rather helps the community forming. Rationalists have it the other way around and frankly I see no way to cure this while still remaining a “rationalist group”. If anyone can solve it, or at least offer possible solutions, this might help the cause greatly.