What this does is frame very limited player agency as correct. Calling any greater exercise of player agency as 'altering reality' makes it something artificial, unwanted. Game-breaking. Note that no exercises of GM authority are ever called this.
we are not saying that limited player agency is correct, and i have a couple of refutations to that, 1) a player can have
lots of agency but a player does not need to be 'altering reality' to have agency, they can have agency interacting with all pieces that the game/GM has already presented to them as they already are, convincing the General you met 3 sessions ago who has no stakes in the fight to bring his armies to oppose the lich king can be agency, 2) we are not framing it as incorrect to have 'world changing' agency, just that DnD is a game where players only have very limited amounts of it in most areas that aren't directly related to their character's personal lives.
But the fact is that there is no reality to alter. It's all made up. It's fiction. Unless the exercise of player agency contradicts something already established, nothing is being altered at all. At best an emptiness is being filled. What's being advocated is an act of creation. Not alteration, not destruction, not reversal: creation.
some of us prefer that when we are in a world, just because the players haven't encountered something yet that doesn't mean there is 'nothing there', the world we haven't explored yet is not an unpainted canvas to us but a painted one that is merely hidden in darkness
My own game Other Worlds allows players narrative authority based around their character's templates (broadly, race/class/schtick) as long as it doesn't contradict something else established. So if you're playing an elf you get to say things about elven culture and rituals. If you're a fighter who used to serve in the King's Army you get to say things about that King and that army. If you're a griffon rider with your own pet griffon you get to say things about griffon physiology and behaviour.
This to me feels so much more natural than 'I don't know, Mr GM what would my elf do when a friend dies?'.
i don't find the three first examples of equal comparison to the latter, the last one is entirely a personal matter, it involves only your character's opinions and expression, nothing the GM needs to have a say in, whereas the first three, you are speaking outside of yourself, you are declaring facts about the world, outside reality is shaped by you saying those things, if you say 'Elfin cries when his friend dies' or 'he shouts and rages at the unfairness' or 'he is silent holding his emotions in check' that has no influence on what the reality happening outside them is,
i see little real difference between being able to say 'XYZ is how griffin biology works' and 'i conveniently 'picked up' a scroll of revivify from somewhere' because it changes what the reality is outside the character.