What is the function of religion?

[Mister Agenda]

I have three questions:

(1) What are/is the function(s) of religion?

To enforce social conformity, codify moral beliefs, signify important events, and provide entertainment. Off the top of my head, not a complete list.

(2) Should someone who does not believe in the truth claims of organized religions (atheists in particular) change his/her view towards religion if it is accpeted that religion actually has beneficial function for a society that our secular age is in danger of destroying?

In the example you give, the only relevant change would be to start believing in the truth claims or organized religion because the religion has benefits, which is a fallacioius argument for believing something is true, so no.

(3) How could these functions, if one remains thoroughly secular in one's ethics and thought, be implemented within a secular framework; should an atheist or a secularist develop a secular religion, and if so, what could it look?

Secular clubs that provide a space to think about morality and ethics, opportunities for networking, a support system, and teaming up for purposes of charitable activities don't have to be too religion-like to provide the relevant benefits of religion, and can be separate groups for different functions. I suppose it depends on how expansively religion is defined. Certainly at least some atheists can benefit from organized community.

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3. I agree with the North Korea example. Absolute devotion and blind obedience with or without a theological component is wrong.

Those don't seem to be necessary components of religion. See Unitarian Universalism.