With or without it, people that are abusive will continue to be belligerent. Data in and of itself is good, and having no feedback to work with is bad when there are multiples of a role, whose job essentially boils down to make this mob's HP go to zero, and individual contribution isn't always so transparent. Sure, a healer also deals with numbers, but the effect of their numbers being low/mistimed equals dead members, which is very noticeable. If you aren't taking hits to the face, or tossing numbers at party members, your job is to make things dead and you best be doing it. Tanks and healers are already easy to evaluate and find mistakes, DPS shouldn't get a free pass or a carry.

In such a situation where no one knows what their DPS is, and a DPS check failed even with mechanics done properly, who are you going to blame? At best it could be one of two, or it's a combination of four players. Would you blame all of the DPS, even though two are pulling their weight and it's one or two players pulling ARR numbers in level 60 content? What if there was an excellent BRD or MCH, but the others aren't pulling their weight, you want to guess who is more likely to receive blame for their failure? In the case of not knowing, blame is blanketed on multiple players, even those that don't deserve it.

It's now a climate of babying a rather important (though unsung) role, where even expecting people to play at bare minimum is too much to ask, and as a great example to illustrate it, A8 a good reminder of that.

On the note of bringing up DPS meters and WoW, in the near decade I've played it, the amount of bullying that I have witnessed that happens over DPS is negligible. Pre-LFD and LFR was best since every one on the server would know if you pulled your weight in runs.