First of all I am part of the "A FORM of Parser" side of the argument. Meaning I approve parser use for personal/FC usage, but not so much of "this is your dps in a random 4-man and should be kicked" side of things.

Parsers are good at evaluating who is under-performing, either intentional, or unintentional. But it could be used for good. Such as figuring out mechanics that you just wiped to and are unsure as to what happened. Or you see another player doing more dps than you are with the same job/gear. Maybe they adjusted their rotation just a bit to eek out a bit more dps. It could also help with who was out of position by using a certain site's combat replay feature.

Do people Fear Monger parses saying X job is under performing....yes unfortunately. But they sometimes forget that people can abuse parses. Look at Summoners abusing the parsing meters on Faust. They may show as being high on the dps meters but they are also intentionally cleaving onto the adds.