Religion

It's like the difference between disbelief and belief regarding deities. Antonyms are just oppositely defined words, as indicated by the use of a negative prefix. Thus, "misunderstanding" is simply an error in understanding, as indicated by the prefix "mis-". The word does not imply an understanding of other things.

It's generally a mistake to try to make them anything other than that, I think.

One can be irreverent without any reverence at all. The word, itself, implies that. Just as "atheism" does not indicate a belief in anything. It is simply the absence of belief in deities or "theism."