My perception is that one drawback of earnestness is that it often comes off as just being boring. The most earnest people I know are not popular. The most popular people I know are more like twinkle-in-the-eye-kind-of-BS-but-not-pathological-liars. I don't mean to say "grr, why aren't nerds more popular!". I mean more that this specific kind of earnestness seems to preclude the playing of certain conversational game…
If you have any sense whatsoever, you intentionally shoot for "boring" while being publicly earnest.
Remember: "May you live in interesting times" is a Chinese curse. There's a downside to being interesting.