If the support's job is to babysit the adc so he can farm for the first 10-15 minutes of the game, while taking none of it for themselves, they shouldn't get flamed for getting a kill. If they contributed to the kill properly, then it shouldn't matter (assists still give gold).
If it was a blatant kill steal, though, that's just bad manners. Seriously, tower-dived an Akali, got the kill, and was about to die to turret aggro with 50 hp left (she did her best) with honor. Then Shaco appeared, ignited me (dumbass), and stole her kill. Considering she was four kills behind, she deserved that one kill on me. But Shaco apparently wanted it.
But generally, the support should be the exception here if it wasn't on purpose. The adc isn't entitled to kills, but it's optimal for them to get it (late-game shouldn't be an issue, since they scale to late game anyway).
As long as I'm not Draven, I usually don't get angry about losing a kill to another teammate.