Friendship and Morality test

So, I want to talk about something that I've pondered on for years, and it has to do with friendship. Here's the context:

There's three friends involved: A, B, and C.

Here's the scenario: Friend C does something to A that A considers really messed up and is hurt by, and now they're not on speaking terms. Friend B then has two options: Not speak to C in solidarity with A, or continue being friends with C because the situation between A and C doesn't concern him.

Now, both options have arguments as to why they're the right thing to do as opposed to the other. Personally, I originally believed that B should side with A because, even if it doesn't concern him, if B knows that C did some wrong to A then the siding with A would communicate to C that B thinks what C did was wrong too and that that's not okay. It would also show a loyalty to A. Furthermore, if B didn't side with A and continued to be friends with C despite how A feels hurt by C, then that to me seems like B doesn't really care about A, or, at least no as much as they care about themselves; like, they'd rather be friends with both still out of their own sake and that to me seems a little selfish. Then the pressure is put on C to make the next move, which would, hopefully, be apologizing to A.

I once proposed this scenario to a friend of mine, and they thought the opposite. They believed that if A asked B to not be friends with C, then A isn't a good friend to ask B to choose friends when it doesn't concern B. Furthermore, because what C did wasn't to B, if B sided with A it would be seen as messed up to C.

But that's kind of why I still think B should side with A; it's similar to the saying "All that is necessary for evil to triumph is for good men to do nothing." Isn't a nobler thing to stand up against wrong doings, especially when it wasn't done to you?

I'm still a little conflicted on what's conclusively the right thing to do though, and am willing to hear why B shouldn't side with A and continue to associate with C. What do you think?

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