Leviticus 5:1 (KJV)
And if a soul sin, and hear the voice of swearing, and [is] a witness, whether he hath seen or known [of it]; if he do not utter [it], then he shall bear his iniquity.
This verse tells me that Christians ought to be both upright and upfront. And one should realize that the Lord will not hold him/her guilt-less for keeping silent when iniquity trumps righteousness with his knowledge, or in his/her presence.
If God convicts one to be confrontational, pray that one has also learned the wisdom of seasoning grace with truth. If one has the power and opportunity to let others know of an error or sin, he/she should utter or reveal it.