The drive towards realism has marked many of photography's greatest moments (Atget, Evans, Arbus, Avedon, Ruff etc). I'm not sure if purity comes into it.
This is the Approved Narrative, at any rate.
There's always been a split between.. well, between somewhat fluid groups. One side, generally speaking, opposes manipulations to some degree or another, the other side taking the "anything goes" approach. The idea that the "greatest moments" have been consistently lunges in the direction of realism is a fairly clear case of history being written by the victors.
We're currently in a very weird position, historically, where the prevailing actual belief is that "anything goes" but the prevailing "heros" were largely somewhere in the anti-manipulation camp. The Victorian-era manipulators, in particular, are widely reviled.
The only substantive argument I have ever seen that opposes manipulation for any reason better than "I hate that guy" is that photographs ought to look like and be photographs, rather than paintings. This pops up here and there throughout history, but nobody ever really tries to make much sense of it, and these days the argument seems to be almost entirely lost. Except for a few fringe weirdos like me.