Most people, even if knowing wrong, would never make any effort to keep other away from wrong doing. They prefer more over to nourish and gain by wrong-doings of others.
Some justify their own faultless by it, to try to gain freedom from remorse by such "he also did, why then not me".
Or catch others by spoken or unspoken hiding of seen faults. In that way the faultfull gets indebted toward the co-doer (by approve)
Or the take it as possibility to win over the belongings or esteem of other, take it as reason to be able to harm him.
Or they don't tell it out of fear to lose profits, prfering to co-work in corruption.
A good person, if telling faults, has no interest on gains, no interest on harm, but simply seeks to prevent from evil actions out of compassion, or as a duty within a relation.
For a person thinking that what ever he does has a right justification, both, the good and the evil advicer, appear alway as enemy.
A wise person takes compassionate criticism or rebukes or forbiddings as a gift, dutyful critique as praiseworthy food for good relation, and even evil intended or uninformed critique as a serious reason to prove it and accept it, if right, even if actually ill-meant told.
Only a person of integrity is intentional capable to advice and rebuke right, only one gone beyong sensual desire, is able to judge and rebuke harmless, and only an Arahat wouldn't fail in any advice and rebuke, yet wouldn't have any further duty to do as well, gives exclusive out of compassion.
So on the way outside the Noble domain and till liberation, there are to kinds of nurishments and denourichments on faults of others:
Avannaraha Sutta: Dispraise
"Bhikkhus, one possessing four qualities is deposited in hell as if brought there. What four? (1) Without investigating and scrutinizing, one speaks praise of one who deserves dispraise. (2) Without investigating and scrutinizing, one speaks dispraise of one who deserves praise. (3) Without investigating and scrutinizing, one believes a matter that merits suspicion. (4) Without investigating and scrutinizing, one is suspicious about a matter that merits belief. Possessing these four qualities one is deposited in hell as if brought there.
"Bhikkhus, one possessing four [other] qualities is deposited in heaven as if brought there. What four? (1) Having investigated and scrutinized, one speaks dispraise of one who deserves dispraise. (2) Having investigated and scrutinized, one speaks praise of one who deserves praise. (3) Having investigated and scrutinized, one is suspicious about a matter that merits suspicion. (4) Having investigated and scrutinized, one believes a matter that merits belief. Possessing these four qualities one is deposited in heaven as if brought there."
sut.an.04.083 | book_042
(៣. អវណ្ណារហសុត្តំ)
[៨៤] ម្នាលភិក្ខុទាំងឡាយ បុគ្គលប្រកបដោយធម៌ ៤ យ៉ាង តែងធ្លាក់ទៅក្នុងនរក ដូចជាគេនាំយកទៅទំលាក់។ ប្រកបដោយធម៌ ៤ យ៉ាង តើដូចម្តេចខ្លះ។ គឺបុគ្គលមិនពិនិត្យមើល មិនស្ទង់មើល (ជាមុន) ហើយពោលសរសើរបុគ្គល ដែលគួរតិះដៀល ១ មិនពិនិត្យមើល មិនស្ទង់មើល (ជាមុន) ហើយពោលតិះដៀល បុគ្គលដែលគួរសរសើរ ១ មិនពិនិត្យមើល មិនស្ទង់មើល (ជាមុន) ហើយបណ្តុះសេចក្តីជ្រះថ្លា ក្នុងទីដែលមិនគួរជ្រះថ្លា ១ មិនពិនិត្យមើល មិនស្ទង់មើល (ជាមុន) ហើយបណ្តុះសេចក្តីមិនជ្រះថ្លា ក្នុងទីដែលគួរជ្រះថ្លា ១។ ម្នាលភិក្ខុទាំងឡាយ បុគ្គលប្រកបដោយធម៌ ៤ យ៉ាងនេះ តែងធ្លាក់ប្រូងទៅក្នុងនរក ដូចជាគេនាំយកទៅទំលាក់។ ម្នាលភិក្ខុទាំងឡាយ បុគ្គលប្រកបដោយធម៌ ៤ យ៉ាង តែងទៅកើតក្នុងឋានសួគ៌ ដូចជាគេនាំយកទៅដាក់។ ប្រកបដោយធម៌ ៤ យ៉ាង តើដូចម្តេចខ្លះ។ គឺបុគ្គលបានពិនិត្យមើល បានស្ទង់មើលរួចហើយ ទើបពោលទោស ចំពោះបុគ្គល ដែលប្រកបដោយទោស ១ បានពិនិត្យមើល បានស្ទង់មើលរួចហើយ ទើបពោលគុណ ចំពោះបុគ្គល ដែលប្រកបដោយគុណ ១ បានពិនិត្យមើល បានស្ទង់មើលរួចហើយ ទើបបណ្តុះសេចក្តីមិនជ្រះថ្លា ក្នុងទីដែលមិនគួរជ្រះថ្លា ១ បានពិនិត្យមើល បានស្ទង់មើលរួចហើយ ទើបបណ្តុះសេចក្តីជ្រះថ្លា ក្នុងទីដែលគួរជ្រះថ្លា ១។ ម្នាលភិក្ខុទាំងឡាយ បុគ្គលប្រកបដោយធម៌ ទាំង ៤ យ៉ាងនេះ តែងទៅកើតក្នុងឋានសួគ៌ ដូចជាគេនាំយកទៅដាក់។