Like you, I have sat in funerals and read obituaries that sometimes seem like utter nonsense. I avoid doing face palms and making moans of disgust, especially at funerals. But I sometimes do an inner chuckle, because I know that no one around me can read my mind. And I'm even more sure that's true of the dead.
The purpose of a funeral is all about the grief of the loved ones, not about the dead, and those closest to the dead probably never did a thing to hurt you. It can be entirely appropriate to present a facade at times, and without feeling a bit guilty either. We do this not only for ourselves, but for others who appreciate it as well.
Imagine a woman at a funeral reception with her fourth glass of whisky in hand suddenly blurting out in a drunken slur how happy she is that the son-of-a-bitch is dead and that he should have been tossed in a dumpster so the rats could feed on him. You don't have to be a genius to recognize how much harm she is doing to herself.