My opinion stems from an idea that I've encountered a long time ago, being that "If your partner was cheating on you, wouldn't you want to know?" I feel like most people would want to be aware of a partner's infidelity rather than not, because it empowers them to act on the situation. Being in the dark leaves them totally powerless.

Beyond just the cheating aspect to it, there's also the issue of health and safety. Everyone has a right to controlling their own sexual health, and undisclosed infidelity removes that right from people without their knowledge. In addition, cheating can be an excellent indicator of a relationship that needs to be ended, or a kick in the pants if you will. ;D And while it totally is more ideal for the cheating partner themselves to be the bearer of the bad news, many people don't for numerous reasons. (Some of those reasons being reasonable for sure.) As an addendum to all this, it's also my opinion that cheating isn't always a relationship ending event. There's always room to work in that situation.

I've been been seeing and hearing a lot recently a number of people expressing the opposite idea of mine, namely non-intervention, which surprised me greatly! Dan Savage is one particular, his view stemming primarily from a place of "It's not your relationship, you shouldn't go mucking about in it." Which I get, but it doesn't seem compelling in the light of wanting to be there to support people that I know and love. I know that if a significant other of mine were to cheat on me the response of someone that had specific knowledge of it being "I didn't think I should get involved" wouldn't be terribly comforting in light of the abandonment that can be associated with infidelity. Am I missing something here?

I mean, I'd certainly only taddle on someone if I have really solid evidence, like specific messages or solid first hand evidence, and only in cases of actual egregious action. (So not for instance if they're flirting or being unusually snuggly.) And certainly only if I know that they aren't poly/have an open relationship. And there's absolutely room for flexibility. By no means am I saying that I have no other recourse than to report cheating, especially if it's it's a relationship I'm close to. All this to say that I'm not foolish, And would do my best to take the action that's best for both people involved, regardless of who is cheating.

TL;DR: I feel that it's almost always my duty to report cheating to the "cheated on" in a relationship, as long as I have good evidence/reasons for doing so. A non-intervention attitude seems unhelpful and potentially hurtful to those being wronged, in addition to health related reasons.

So please change my view! I'm very interested in hearing alternate viewpoints here, both because it's so clearly opposed to my own view and I was very surprised at the number of people out there that disagreed with me. Thanks CMV!

Small Update:After reading through these generally great replies, I've been given a lot to think about. I was planning on taking this talk to other people in my life that'd have good opinions to share about this topic, but now I'm reconsidering pending some reconsideration. While I wouldn't say my view has definitively changed, I'm glad to have been give a lot of really solid counterpoints to what I believe. Thanks so much CMV!