Mr. Cutcliffe has given a good answer to this question, but one more consideration is noteworthy. Consider the problem of natural suffering: Why did God invent the horrors and agonies of ebola, cancer, tsunamis, etc? This problem is far more pressing in monotheism than it is in either polytheism or atheism. read more
Monotheism is believing in one god more than atheism. Polytheism is believing in more than one god more than atheism. The difference between one and many, and between none and any, in this case, is trivial by comparison. Whether you believe in one god, three gods or 500 gods, you're a theist. read more
Monotheism is "closer to atheism than polytheism" is only in a purely numerical sense (number of gods whose existence is claimed or acknowledged, where zero is closer to one than it is to 3 or 12 or 144), which is fairly ridiculous way to compare the three. read more
Conversion to monotheism from polytheism is generally rapid and pervasive, while the same just doesn't happen in reverse. This indicates either that monotheism is closer to the truth than polytheism, or that the Torah grants a mysterious evolutionary advantage to its adherents. read more