Is it rational to be irreligious? I personally strongly believe that it is not.... See here for a discussion. There is obviously a lot more to say. Chazal put it well about a person who sins - אין אדם חוטא אא"כ נכנסה בו רוח שטות. Temporary insanity.
And remember, NOBODY is 100 percent religious. There are 86,400 seconds in the day. Of those, for how many are we truly religious? How many of those seconds are spent being aware of G-d's presence or serving Him in some way? The pasuk says that in order to be truly religious we must שויתי השם לנגדי תמיד - Place Hashem before us always. I don't know too many people who are religious for all of those seconds. So just as it is irrational to be secular [as detailed partially in the article I linked], it is all the more irrational to be religious part of the day and not religious for other parts. If Hashem is then He is. If He isn't [ח"ו] then He isn't. But He CERTAINLY isn't only on duty part of the time when we are conscious of Him.
So a GREAT Avodah for Elul is to make ourselves more G-d aware - ALWAYS [to the best of our ability and with pleasantness and simcha]:-).
