You dont seem to be doing to great at understanding where the people who speak up for parsers are coming from either - and even though I know it probably wont matter since you seem to have made up your mind, let me try to explain why I dont think that MSQ or leveling content are so much different from raids and Extremes.
Let me preface this by saying that any abuse or harrassment is never okay - its not okay to insult someone over their numbers in Sastasha, but its equally not okay to insult someone over their numbers in E4S. Can we agree on that?
Now, with that out of the way I'd like to circle back to my point about "everyone needs to put in a content-appropriate amount of effort" - obviously Savage will require a lot more effort than a leveling dungeon but even the very first bat you encounter in Sastasha wont just drop dead if you wait long enough - well, it might, if you let your teammates kill it. As your level increases so do the expectations the game and your fellow players have of you - as is actually the case with most RPGs: The further you progress the more is asked of you. A single player game will let you know if you're not doing well enough by showing you a "Game Over"-screen. By its nature an MMO doesnt do that because there are other people who might pick up your slack, often without you - or them - even knowing.
A parser, providing you with numbers can give you that feedback and allow you to actually improve so you can play in a way that leads to you clearing the content with your group instead of having your group clear it for you.
I dont think it matters much in what kind of content we're talking about since I dont believe in carrying people no matter what the content is.
Why should some just get a pass and not be asked - in a friendly and polite manner - to be put in the level appropriate amount of effort just because its not the most difficult content in the game?
Why should it be okay for someone to be lazy or refuse to learn just because they're in a leveling dungeon?
You suggested to try to understand where a person whos against parsers in leveling content is coming from and all I can come up with is that that person must think something along the lines of "I know I'm really bad at this job, but I cba to learn it properly, its just a leveling dungeon anyways so why should I care about playing well in the first place and no one will ever know anyways" - so because of that thinking they are concerned about parsers being added.
Or maybe its people who believe that they're doing really, really well - and dont want to risk seeing that belief destroyed by facts (you know, kinda like what parsing people have been accused of before: Getting an ego-boost because you're doing well in a videogame - only those people dont actually want to know how they're doing, because it could be some ugly truth waiting for them).
Some might actually be concerned about harrassment, but in regards to that I can only repeat what has been said time and time again: In my personal experience - and apparently the experience of other people aswell - people who show that they're making an effort and are trying their best dont get harrassed. As I mentioned before: personally I cant recall a moment when someone in a random DF-run was harrassed about parser-numbers, so its probably not a likely occurence.
...so yeah, I'm afraid I cant understand the mindset of a person whos worried about others finding out they're bad at the game but doesnt do anything to change that. Sorry, cant wrap my head around that. Not even considering that this is "just" a game and that people might only play it to see the story.
I'd like to see things from their perspective, but I'm afraid I cant since I dont share this mindset of "Oh, its just a dungeon, so nothing really matters!"