It seems that there is a lot gray area where many authorities in the J-blogsphere disagree on when and how one can/should go off the Derech. Therefore, as a public service, I have compiled a little guide, a Kitzur of the main opinions regarding the issue.
It seems that XGH holds the most stringent position on the matter, while Daas Hedyot seems to be the most lenient. Somewhere in between these two extremes held by such prominent Halachic figures, we have other luminaries like BHB, Yeshivish Atheist, and others who fall somewhere in between. Although it seems to be pretty clear that XGH is the most stringent, it is not clear what exactly are the requirements one has to meet in order to Halachically go off the Derech. There are some definite rules that we can pinpoint:
1) You can not be Chassiddish, Lubavitch, Yeshivish, Baal Tshuvah, Mizrachi, under twenty, over forty, amongst others.
2) Even if you are lucky not to fall under any of the above categories, you can not be an atheist once you do go off the Derech, have any difficulties in your social life, or have any other "abnormal" situations.
3) You have to have been raised Modern Orthodox, been to Israel, have Zionist sympathies, gone to movies (very important it seems in XGHs estimation), and been able to do anything you could do if you are off the Derech.
4) If by chance you have met all the above requirements, you can still not go off the Derech according to XGH. You are to normal. You must come from an interesting background like Chabad, crazy Yeshivish, or some other fanatic sect.
5) If by some defiance of all natural laws, you are still qualified, there is one more caveat: you really are not allowed to go off the Derech, you can just become Orthoprax. Yes, you heard correctly.
Some have criticized XGHs position based on the impossibility of it ever being borne out in practice. To which there is a very good precedent one can respond, namely עיר הנדחת, and בן סורר ומורה. But some have answered in the spirit of the aforementioned Gemorah: Certainly this Halachah is applicable in practice, and the proof is that "אני ראיתיו וישבתי על קברו" I saw him and used to comment on his blog. והמבין יבין
According to Daas Hedyot, anybody can go off the Derech for any reason at anytime. וכל המרבה הרי זה משובח. Especially if you become Roman Catholic, because what's more logical than switching from one fundamentalist religion based on myths and unsubstantiated fairy tales, to another religion based on myths and unsubstantiated fairy tales. Mamesh, I don't understand why anyone disagrees.
The most curious opinions are the approximate range into which BHB and YA and others fall. They have this curious requirement of having one investigate the alternatives and 'think critically' for oneself.
In summary, the last opinion can be discarded outright because we have no precedent in Halachah for anything even remotely similar to these requirements. "Think critically" who ever heard of such a thing. As to the forst two options, I favor XGHs position since it isn't even followed by its own proponent, something that we have lots of precedent for in Halachah.
Now, obviously this is all הלכה ולא למעשה, and each person should ask their Rav, especially on such an important matter: How to go off the Derech according to Halachah.