Why do the nonreligious allow Christians to claim the moral high ground when the US is the most religious industrialized country yet has the greatest per capita rate of homicides and assaults in the industrialized world? Is it because the media allows these proclamations of morality by Christians go unchallenged?
Christian can claim the moral high ground, and other people can and do point out the absurdity of that claim.
From the Land of the Convict, it seems that a lot of the news outlets in the (dis)United States of America are in the pockets of those religious fundamentalists.
It;s the power of umbrage. When morals are discussed outside of a religious context the religious are free to interpret that in a religious context. Perhaps they don't even realize that they're in a secular discussion. When the idea of morals without religion is explicitly discussed then the non-religious are happy but the non religious are vocally upset and claim oppression. They are afforded a platform to decry their oppression. They purveyors of the thought they dislike lose audience and so you hear about it less. When it comes to the idea of morals being exclusively the purview of the religious then of course the religious are comfortable with that. But this idea only gains mass media acceptance where the non-religious are unable to claim the same, when the overton window does not afford them a platform to decry their oppression. Ironically it's the difference between claiming oppression and being oppressed.
I don't think it does go unchallenged. But superior morals is part of Christian indoctrination and any claim to superiority assumes rights of control. It becomes part of the reward for Christians for sacrifices of their belief.
Their morals are of convenience only.