It’s actually a lot more specific than that. There are precisely argued theological arguements for individual beliefs, tenets, and socio-political positions and for why they are or are not dictated by a given religious group. So while fundamentalist Christian groups argue for the literal interpretation and acceptance of every dictate in the bible (or from whatever religious hierarchy is in place), that usually isn’t actually what there doing. There’s a fair bit of intellectual masturbation, and historical trend involved in establishing which beliefs, edicts, and dictates “define” a given faith group. Mixed up in all that there is actually a specific approach that involves tying whatever particular features define their group as being essential to belief and membership. So it isn’t so much that denial of evolution is a marker of membership, but that the concepts behind evolution contradict major bits of what is considered to be essentially to their faith. The whole structure of how those belief systems are built and rationalized rests on a sort of checklist of interlaced ideas. Abandon, disprove, or even question one and it must as a matter of course mean you reject the whole edifice. Now your the bad “other”. In other words I think it goes in the opposite direction. Rejection of evolution draws naturally from their restrictive approach to belief, as opposed to be an easy political marker for membership that gets justified later.
And that kind of thinking isn’t unique to conservative or orthodox sects. Oddly enough a lot of left wing, Main Line Protestants seem really, really, angry at Unitarians. And don’t consider them to be Christian. I worked for a brief while at an incredibly liberal, non-affiliated Theology school. The students and the faculty were like conducting Unitarian hunts. Searching them out. Accusing people of being Unitarian. And constantly griping about a pernicious Unitarian influence on the school. It was pretty bizarre.
I’m just gonna say please don’t. This, frankly rather basic, arrogance from religious folks is at the heart of a lot of the prejudice we atheists (yeah bro) experience day to day. Its easy enough to hide, and coast on the assumption that all people (except those people) are religious. But I’ve been told to my face that I can’t be trusted around children, don’t or can’t feel love, must not have any friends, don’t REALLY have family, am actually a murderer, will be a murderer and a dozen other things. I’ve been kicked punched and spit on. All driven by the false and arrogant assumption that only religion provides a person with certain basic things. Whether that’s love, answers, community, or just status as a human being. Those things that religion “gives back” to you? That’s not a feature of religion. That’s a feature of society. And you can get them from all sorts of places. My family, the guys I go drinking with on weekends, the people I troop around with looking for new foods to try, my friends improve troop, a book club, The Church of Satan, the ACLU, a bunch of idiots you talk to on the internet, your neighborhood, a business where you are a proper regular, and yeah even something to do with science. There’s nothing unique to religion that provides these things. You’re religion doesn’t care about you (that’s like saying literature cares about you, or linguistics cares about you) its the people in your religion that care about you. And the social structures that are common to human endeavors that re-enforce that care, and allow you to see it.
So please don’t infantilize or dismiss people you disagree with because you fail to see how we can exist in society without some undefinable thing you like to think your getting out of your particular in-group. Its just arrogant and insulting.
Beyond that you’re just embracing the whole science vs religion thing. Science is not a belief system that is in competition with other belief systems, neither is it intended to provided the same sort of moral guidance or approach the same sort of questions and ideas (that would be philosophy). Unless your religion specifically denies science, or from the other side: your an anti-religious person with a nut on for attacking religion using science, there really isn’t a conflict there. At all. Really. Science in general, and the scientific method is specific, comes to us from religion after all.
It’s not intended to offer “anything back” in the nebulous warm feeling sort of way you intend. Otherwise it offers back the internet, modern medical science, guys on the moon, and silly putty. And a complex frame work for evaluating the veracity of subjective experience. While I may hold certain things to be true now that may be disproven eventually (this happens to me nearly weekly BTW), at no point does that impune science, the scientific method, or the skeptical approach. Because that’s what its for. All we’re talking about is a carefully constructed, rational, rhetorical system for examining the world around us (the real physical world) and arriving at something objective at the end. Its very much supposed to change, reverse itself, purge old false ideas, expand, and repeatedly test and question everything its been used to find thus far. Forever. So even if everything science knows now changes tomorrow, science will still be there. Because the base approach not only still works it’s what will allow us to know we’re wrong.