How would they become more blurry? Right now you can say "You're performing really badly!" and that's not considered harassment. Then you could say "You're performing really badly: your DPS is only 2500 when it should be 4000!". And again, if you add any personal insults or bad language to those, they'll turn into harassment, despite if numbers have been used or not. The main difference in my eyes is that when the numbers are used, the person receiving the critisism will know if it's based on facts or not.
They are different arguments. I have personally witnessed parsers being used for good in this game for many years, and I have not yet witnessed a single case of parser-related harassment despite running endgame in this game from 1.0. On the other side, what I see this thread is people speculating about the possibilities of there being parser-related harassment that would somehow appear out of nothing when the official parser would be added. I have not seen this argument being based on even personal experiences from this game (I may have missed a post, of course). Furthermore, the people most fervently arguing against parsers don't even seem to be doing any content in which they are relevant, so the discussion doesn't really even concern them in the first place.
How exactly is this different from all the current "high DPS or kick" party finders?Do you think that those people are right now just eyeballing if their party members are pulling enough or not? Furthermore, what exactly would be the issues with these party finders? Players are free to form whatever type of groups they like, and we all have the freedom to choose to either join them or not to join them. I don't join "high DPS or kick" or "one mistake and kick" groups now, and I would not join "4k DPS or kick" groups then, even if I would meet the requirements. And I would not suddenly change the requirements for my own party finders (which are currently something in lines of "be comfortable with the fight and your job and bring patience and good attitude") just because the parsers people are already using would be made visible.