One half of your argument is that public parsers will turn more people into jerks, and increase the rate at which people are harassed in content by their mere presence. And the quote listed above is the very crux of the other half of your argument.
You hold to this idea that the group should be beholden to the comfort of the individual. Killing one target at a time, killing smaller packs instead of larger packs. You think it is the prerogative of the individual to be allowed to play how they will in DF, based on what makes them comfortable. This seems also to extend to the amount of DPS being done and whether it is sufficient to clear content. One simple way to explain how you couldn't be more wrong, is that SE has proclaimed that it is entirely acceptable to kick people out of your group because of differences in playstyle. This means that if a tank "didn't want to pull everything because they weren't comfortable doing it", and the rest of the group wants them to, and they refuse, then they are 100% legitimately able to be removed from the group because the way they way to play conflicts with the way the group wants to play.
You talk about the DF as though it is inherently a mixed bag, that you go in having no idea what you will get, and that if you don't like what you got, you should have gone in with a premade. The reality that the precedent that SE has set is the exact opposite. If me and a buddy go into a DF together, and we get a tank that wants to pull small packs and kill 1 target at a time, then we absolutely have the prerogative to vote kick that tank from our group in hopes of finding a tank more suitable to our playstyle. We also have the option to try to convince the existing tank to play more how we want to play. It's up to us! In this case, the will of the many outweighs the will of the few. And SE stands behind this idea.
You repeatedly parrot the idea that the onus of how you play in DF is on you, and that if you want strict control over how your Neverreap run goes, you have but one option: go with a pre-made. That simply isn't the case. The onus is on the individual to play how the group wants to play, not the other way around. The individual can either play along, leave themselves, be tolerated or be removed. BUT, regardless of their choice, if the group wants you as a tank to do big pulls, because there are two heavily geared DPS and a healer in the group to support it, and you refuse because you're not comfortable, they ABSOLUTELY have the option to vote kick you out immediately.
So, disregarding issues of tank playstyle, this same concept extends to DPS as well. If someone is doing 300 DPS in an instance and the whole group has something else in mind (i.e. a quick clear for daily expert roulette), then that 300 DPS player can either step it up, be tolerated or be removed. The onus is NOT on the group to tolerate a low DPS 'bad' player simply because you can eventually clear content no matter how awful they are. The group has the means and the justification to remove said player from the group.
Whether individual or public parsers are introduced in the future, or neither, we still have unofficial parsers. People are still going to use them, whether SE implements one of their own. The main caveat is that you have to keep it on the downlow, or risk being punished as a result. Nearly everyone who parses has grown accustomed to this reality, and what ends up happening is that rather than confronting the offender and explaining the issue, they must remain silent and basically have two options: tolerate or kick. Even if nothing official is ever introduced, people will still parse and this will still happen. And to me, that's a shame. This corner people are being forced into is very unfortunate. For a good many people, having the tools and knowledge that comes from parsers would allow them to find the gaps in their play style and improve. They would have the context of knowing how their gameplay compares to others, whether how they perform is good or bad, acceptable or otherwise. But right now, mainly due to the fear of what would come with the introduction of a public parser, people largely remain ignorant.
To me, willful ignorance is never a good thing. There is no amount of hurt feelings and disappointment that can counteract the negative impact on the community by willfully forcing them to remain ignorant about the reality of DPS being done.
Yes, it is true that the introduction of public parsers would increase the amount of harassment and kicking that occurs based on subjectively low DPS. Sadly, jerks will always be jerks, regardless of the scenario. This makes it easier for some, which is also true. However, on the flip side of that coin is all the positive benefit you can reap by suddenly enlightening a community of people that have been unwittingly dwelling in the dark, unable to know or conceptualize the metrics behind their performance. They will finally have the opportunity to see how well [or not] they are doing, and have the tools necessary for learning and improving. The influx of knowledge that public parsers would bring would be absolutely immense.
For those concerned about the abuse.. well, you still have the option to report harassment, just as always. And people who would harass because of the knowledge that public parsing brought them should indeed go punished, just as they do now. But to think the system would simply collapse because of the presence of this knowledge, that the DF experience would be inadvertently ruined because people actually know what is going on, rather than remaining clueless, is completely unfounded. Turn to example like WoW, who have always had the option of supported parsing and see how this doomsday scenario that you and others like you repeatedly parrot, simply does not occur. You have no basis to claim that if SE were to introduce them into FF14, that the scenarios you describe would occur. You repeatedly say 'prove it' in reference to people saying that it wouldn't, and that is simply inane. Why is the onus on the people who disagree with you? How do you get off claiming one reality, and then turning around and refuting another possible reality simple because they cannot prove it. What makes your point of view superior? The answer is nothing, because it isn't.
Nobody knows exactly what will occur, all we can do is look at similar games with existing implementation of public parsing to see how things worked out. All evidence points to the reality you describe not occurring. All of the fear-mongering that goes on in this thread has absolutely no basis in reality. We all have to make educated deductions about the future of the game in respect to the introduction of parsers, but there is no evidence that points to the scenarios you describe becoming true. In fact, all of the evidence points to the direct contrary.
Parsing is simply a means to an end: the attainment of knowledge. Why would anyone in their right mind prefer to leave the masses in the dark... ignorant and unwilling to move forward, simply to avoid the punishable behavior of a small minority? There is such an insane wellspring of improvement waiting to be tapped, and the only thing holding it back is the fear that a small minority of under-performers would become uncomfortable with facing the reality of what they are.
How much DPS is enough DPS is completely subjective and is to be determined by the people who you choose to play the game with. You can solo all of the quests you want, and never once be questioned about your DPS, but once you step foot into the public domain, once you opt to participate in DF/PF, you subject yourself to the will of the group. And if the group deems that your performance is lacking, it is their prerogative to remove you from the group or tolerate your performance. But they are never subject to your will alone, and that is why public parsing will be a largely net benefit to the community, as opposed to a detriment.