I don't think atheists would have a problem with anyone treating the Bible (or any religious text) as literature, since there would be a lot less religious violence in the event that religious doctrine couldn't be cited as an absolute authority.
But, many modern Christians insist that the Bible must be taken literally, and that it should be taught as science, or presented as an alternative to science. Those are the people atheists are making fun of, and they deserve the ridicule.
> If you just dismiss these religious texts as opium for the dull medieval masses, you might miss some deep poetical truths about mankind that just cannot be stated explicitly because of the shortcomings of any human language described above.
What Karl Marx meant by that is not that religion makes people stupid and compliant (although sometimes it kind of can,) but that people use religion to soothe the burdens of life in an unjust and cruel world... and that the illusory comfort offered by religion often stands in the way of making real societal progress. People who believe that God alone will punish the wicked and reward the righteous and that every event, no matter how capricious or unjust, is part of some divine plan, will simply tolerate the world and trust God to change it, rather than try to change it themselves.
And yet much of what could be considered progressive moral change in society has occurred in spite of religion, either through secular or scientific ideas pushing against religious authority and supernaturalism, or through reform within the religious community itself.