One of the most common "I know it's a delusion, but I need it" arguments is the one in which the believer states that he just can't live with the thought that his life has no meaning and that we are just floating in space.
I think this one is also an admission of the fact that religion is really a statement about the ego of the believer rather than anything else. Why else would someone need to feel like his life has cosmic importance? In other ways, however, this one perplexes me because our lives are full of meaning without any need for a supernatural friend with a plan.
This is simply and obviously because we have each other. We could all spend every spare second trying just to take care of each other and still not be able to do the job as well as we should. Just spending that time on our friends and family would leave us no time to contemplate imaginary friends.
The fact that we don't do that and that so many of us feel such a disconnect from those around us says a great deal about us--and what it says isn't really good. But, that is the subject for another post.
The weakness of this "argument", aside from the fact that it is just a plea to leave them alone with the delusion they so desperately need, is that it is such an inadequate delusion.
Life has just as much meaning whether a person believes in god or not. What does change is how the person spends his life. Rather than spending his or her time and resources on things that are undeniably real and could therefore have an undeniably real effect on the person or those he cares about, he or she is spending time and resources on things that don't appear to have any basis in reality.
Furthermore, the delusion seems quite inadequate to the stated need. If there is a god, then we are merely his hobby. He doesn't need us, after all, he's a god who can create whole universes. To me, the thought that I might be the hobby of some invisible magical being gives my life less meaning, not more.
It is much more disheartening to believe such a thing than it would be to accept that we don't know if there is any cosmic purpose to our existence. I think it is far more grand and glorious to accept that we are just what we seem to be: one of the many forms in which matter and energy manifest themselves in the universe. The stars are simply conglomerations of matter brought together by gravity. Are they any less wonderful because of the simple mechanics of their formation?
You can choose to reply to the "I need to believe to give my life meaning" argument with the following:
"You realize that you are simply admitting that religion is a delusion you need for emotional purposes--to make you feel good about yourself?"
"I don't see how believing that I am the hobby of some invisible magic being gives my life any more meaning."
To that one you can add an explanation:
"A god who can create the universe can do anything he wants. He doesn't need us. We are a hobby. We are what he has because he can't get cable TV."
"My life has plenty of purpose without needing to believe I am cosmically important. I would rather spend my time, thought, and energy on things that I know are real. I know they are real because I don't need faith to believe in them."