I can somewhat understand OP's question, and I'll engage in good faith because I immediately thought of someone who might fit the bill.

I know someone who plays BLM. He only recently started doing savage with a static made up mostly of people in our FC. It was supposed to be a "just for fun, let's see how we do" type thing. Two of the people in the group are also in a different "hardcore" static, and their gameplay is at a pretty high level. They use a parser, and so my BLM friend started using it too because he wants to work toward that level. Fine! Good luck! But since he started using the parser, all he talks about are his numbers and how he's consistently behind top tier BLMs. He obsesses about it, tweets about it, talks about in in game etc. A few weeks ago he basically had a small breakdown about it because he isn't able to close the gap. IMO, he's a person who really shouldn't be using a parser because it's clearly making the game less fun for him.

As for the larger question of parsers in general, pretty much all there is to say has been said. For some people, seeing performance and tracking improvement are important. For others it is not. People using parsers should not affect your own enjoyment of the game, and if using one yourself is making the game less enjoyable, just stop! As for myself, I know I'm not pushing huge numbers, but I also don't care. It's not the parser's fault! I've had exactly one person ever tell me that my DPS was "bad" and I did not report them or respond with a bad attitude. I took a screenshot of their hideous glamour, and me and my friends roasted them for a good ten minutes. Them "informing me" about being "bad" had no effect on me because 1) I already know and 2) Even if it were new information, my time is limited and I'm not about to put much time into optimizing my gameplay because I've reached a level where I am "good enough" to consistently clear the content I like to do.