To speak or not to speak - that is the question

When pondering a encounter that occurred nearly two years ago I remember this: being shocked to learn something that is not okay by society's standards and even more so being shocked to know this when some very much closer to it were clueless.

Which leads to the question of which is better:
To know or not to know?

Would it be better to know the wrongs of those who live around you and shape your life and who's behavior you mirror OR to live in blissful ignorance about an occurrence you never knew to happen by a person you wouldn't suspect it from?

What if others you knew, who didn't know the person as well, knew of the actions and not the person?

To be perfectly honest I was happier not knowing but upon knowing I was better able to judge character and explain several other occurrences. But I was not effected daily... In those circumstances is painful knowledge worth knowing?