And that's all well and good, but I still don't think that and levity are mutually exclusive.
They're not in general, although I think that levity, like solemnity, may have negative connotations for some people (for example, one of goofing off). It all depends on context, and also on history. Surely you've encountered people who use the expression "lighten up" inappropriately, dismissively, as a way of saying that a person or their ideas don't deserve to be taken seriously. But that's a digression, at least I hope so.