I don't think many religions actually condemn weed, at least originally they didn't. For example, in Morocco hash is traditionally the preferred alternative to alcohol which is condemned in the Qur'an. The Bible doesn't really say anything specific about whether weed is a sin or not, but we see Jesus turning water into wine so clearly the idea of intoxicating chemicals is not incompatible with Christianity. Eastern religions, well, they're not really so concerned with calling things "sins" like the monotheistic religions. Many Native American beliefs make use mind-altering chemicals religiously, such as peyote among the Navajos and psilocybin mushrooms among the ancient Aztecs.

And of course, my own atheism has no problems with my pot habit at all.