What can religion teach those who vehemently oppose the notion of God? In my opinion I can't think of anything. Both belief holders and atheists sides, the more conservative orientated are dogmatic. There's is the only way and if you disagree you are not seriously seeing truth correctly, are wrong, are an idiot or a sinner going to hell. This is of course those who are most dogmatic in their beliefs and not open to other lines of inquiry, faith or different belief system. In this case, subjective emotion -based opinion, judgment and labeling furthering a divide between us and them.
This accomplishes nothing. It takes one away from the table of discussion. They are ruled by their passions and are not clear headed enough to engage in critical thinking dialogue. They are a resistance to both change and problem solving. They are an island unto themselves and in a blind box. They don't care and can't readily be reached.
I am agnostic. To answer the question religion can teach basic philosophical principles such the like in Buddhism but not is hard core against religion of any sort. I take the good from what one can find and ignore that which is not fruitful or to dogmatic. People would commit all manner of evil with religion or without. My problem with religion is it tells you what to do but there is no codified way to practice and instill these core concepts so that they are actually lived by.
I can't stand the hypocrisy in religion and people hiding behind it due to rationalization, denial and judgment of those not on their path. I try to meet all on an even playing field and as I said learn what I can from different perspectives. I try to be open minded with another belief system. I look for communication over differences. In other words more walking the talk than merely what anybody does believes in or not.
Religion involves a subject of devotion and a frame of reference towards reality, including a system of values and ethics, in theistic religions the subject of devotion is a deity or divinity, in non-theistic religions the object of devotion is going to be something else, enlightenment, transcendence, knowledge whatever.
Even of the theistic religions which have God as a subject of ultimate devotion there's a lot of distinctiveness to the different schools of thought, I've read some interesting accounts of God and divinity which consider both to be synonymous with humanity, all the writings within the bible about if you want to love God then love your neighbor, that every individual human being is the living image of God, joined up with a quasi-mystical or pseudo-religious understanding of psychology, individual, social, conscious, unconscious.
Jung thought that there was a dialogue or dialectic between the divine mind or being and human minds and beings, its part of how he accounted for what appears to be the growth and change in God which appears to be simultaneous to that of human kind throughout the old and new testaments leading up to the incarnation and death/sacrifice of God their Godselves in the person of Jesus. Which lines up pretty interestingly enough with some of the kabbalistic ideas about the 32 just men, one of whom can emerge as the messiah at any given moment but are likely to be killed for doing so, like the prophets and Jesus in the old and new testament.
Those ideas to me are interesting because they bridge the gap, for me at least, between materialism and supernatural accounts/beliefs, though they'd be total and utter heresy to some more narrowly doctrinaire believers, and possibly equally to some more narrowly doctrinaire athiests for whom not even mythology or mysticism can serve any purpose what so ever at all.
Anyway, in both of those conceptions the idea of the deity, to which devotion is directed, is such that it effectively calls for a more general devotion to all humanity, which puts the ethics, norms, mores, values of believers and society into a new context, they make sense because all those questions relate now to how do you practically be devoted to God, is it prayers, church attendance, how often you invite others to your church (or to adopting your personal creedo as their own) or is it a matter of being related to neighbours and other human beings through systematic values, ethics and knowledge of human nature.
Even if a religion has that weird divorce between the deity and paying them homage and worldly or temporal ethics and values, which is weird to me, very, very weird, those same schools of thought, for the most part, involve some sort of benefice and benevolence towards all things of God's creation and others like your self. So there's a role, it plays an important function and has for the majority of people for the majority of human history, that's not to say numbers trumph reason, its just to say its served a lot of people well to this point, the rate at which its challenged, questioned and forsaken I actually dont believe would have been possible without the religious ground work done to prepare for such a state of being in the first place.