Two different things.
History, last I checked, is rife with religions and religious figures, as it should be if it's a factual history class. History is taught, it's the science of the past..i.e. as evidenced through observation. Religion is also discussed in the science of politics, often as a tool for oppression, but again, this is teaching politics, not religion per se. Government classes aren't really "political theory" classes. Those sorts of classes tend to be college-level. As is philosophy, the philosophy of religion, etc. The science of economics, I can't think of any reason one would need to teach about religion, other than to note that it's a form of business, etc.
You, however, seem to be suggesting that "teaching a religion" at a public school is OK. It's both indefensibly ignorant, and unconstitutional. What would you be teaching? Nothing. OK, so you favor teaching nothing, but which flavor of "nothing"? Which religion? Leave one out, you aren't teaching them all, you're choosing religions as a publicly funded institution, you're back outside the bounRAB of the constitution. Is that what you're advocating?
Historically, sure, even Napolean comments on it:
Napoleon Bonaparte
"Religion is excellent stuff for keeping common people quiet."
"Religion is what keeps the poor from murdering the rich."
"All religions have been made by men."
-Napoleon Bonaparte, French emperor
-Mach