Expert on rehabilitation of water streams made an effort post (and then several very patient replies) about how stacking rocks is harmful.

Bunch of users freaked out, as if their life depended on rock-stacking. They tried to rules lawyer how close to a water stream you had to be, for it to be bad. They pulled the old "indigenous people do it!!!" defense. They tried to argue that the user was making an individualist argument and thus a capitalist and wrong. They tried to argue that "they just couldn't see how it was bad, so the expert on water stream rehabilitation is wrong and/or overreacting". They tried to play it off as "well it's not bad that i do it" despite having had explained how in this very specific situation, it was actually an individual problem and something they also should not do as individuals.
People brought up "take nothing but pictures, leave nothing but treadmarks" (basic how-to-not-be-a-dickhead-in-nature-etiquette) which these users also then freaked out about.
A lot of these users were power users on the site and their reaction and subsequent attempts to rules lawyer and then attempts at playing it off as a bit/something silly was very disappointing to see and it therefore still frustrates me, because they behave as if it was totally just everybody overreacting, and not them being beliggerent assholes, for which they should apologise.

Consensus was that stacking rocks disrupts water streams and does a lot of weird shit for microorganisms, soil, erosion, bugs, that sort of stuff, so touching rocks is bad and stacking them is worse. Can't recall more than that, but basically: Things in streams are used to rocks not moving about a lot, and they are so used to it, that even just a widdle bit of rock-moving-about done by an individual, is very harmful.
I have no idea wether they should be knocked over or not, but I would assume so, since the wind probably does it otherwise. I dunno about that, not the expert.