Many times when I play Tahm Kench support, I eat a low-health ally and get them out alive. However, there are times when I do this only to have them flame me because they were "about to get a kill". In a chaotic teamfight where health bars are bullet trains to hell, it's hard to know exactly whether or not this teammate will kill a low-health enemy with the 0.2 seconds they [this teammate,] has left alive. I have to make an IMMEDIATE decision of what split-second I choose to evacuate them. Okay, so I make the save, and then: "report tahm assisting enemy team". So the next time there's a similar situation, I try to give this teammate a little more time to execute the foe, but the teammate dies: "why no eat me", ensue Missing Ping spamming over my head.
It's the pessimism that bugs me. If I make a save but accidentally deny a kill, I'm 100% a traitor rather than a sincere, team-playing support who makes the occasional mistake. Perhaps some of you have times when once you make a mistake, a teammate blames you for intended treachery.
I think a big reason why many players are anxious about playing Alistar is because if botched, his W-Q combo can knock an enemy to safety; it's immediately treated as intentional because that's what cranky kids do. Same goes for Vayne: if your Condemn missile is flying toward your target, who flashes away from a wall at this time, getting knocked to safety, you're treated as "trying to save the enemy". It's the fallacy of seeing an unsuccessful result and believing that therefore, the contributing action was perfidious: there are those that win and those that betray. Folly.
The scapegoating can proliferate in these situations, with blamers and their teammates beginning to scrutinize the botcher for any tiny mistake they can potentially blame for the game's loss. Blamers build cohesiveness with other witch-hunting teammates in order to forget that they're part of a losing team, convincing themselves that they're, instead, part of a group that doesn't screw up.
I'll conclude with an interesting phenomenon that occurs once I get accused of treachery: I become reluctant to save whatever teammate accused me of it. Generally, I will save them but my save's usually clumsy, late, or hesitant, as I feel that this person doesn't deserve the save and that they'll most likely reply with something far from gratitude. Teamwork is not solely champion synergy and coordination, but its own mentality and language.