That's not the question.
The question is "Who gets harmed by making the story quest optional?" and the answer is "No one".
Even Yoshi-P has said that he's fine with people "fast forwarding" through the story. Putting that in TV terms, that'd be like watching all 28 (or whatever) seasons of the Simpsons on 30X speed.
At that point, WHY even have them do it?
Yeah, because people couldn't enjoy the challenge of playing Pac-Mac without first watching a 40 hour cutscene about what led him to be in a maze, eating dots and being chased by ghosts, right? :P
I hate to raise this comparison, but how do these people feel about gay marriage? Obviously, it's a much more important issue than that of a video game, but the same basic principles are being argued, here.
People are arguing against something that has zero effect on them (in this case, making the story optional) because...it makes them feel bad?
There is seriously no other reason.
And I can't wait for someone to play the "I'm offended" card on this. People who have no argument will never pass up the chance to act like they're offended because it's the only way they can see to try to add weight to their argument (hint: it won't work).
If you agree on the first point, good, that's progress.
On the second point, there's no argument against it, aside from the exact same rhetoric spewed by people who were against gay marriage.
Seriously...
"People shouldn't be allowed to get married because it ruins my marriage!"
"People shouldn't be allowed to skip the story because it ruins the game for me!"
Again, nowhere near as big of an issue (and I'm glad the supreme court finally did the right thing), but it's the same exclusionist logic at work here.
If someone enjoying something their way ruins it for you...well, what can be said except that you're a terrible person?
And what people like you fail to grasp is that people want to have the choice, and right now, they don't: it's either grind through 10+ hours of something they're entirely uninterested in, mashing the esc key the whole way, or they don't get to play with their friends.
If they want to grind dungeons, fates, leves, etc, WITH...THEIR...FRIENDS, that should be their CHOICE. After all, the MSQ basically separates them from their friends for 10+ hours, with the exception being the instanced content where their friends can at least come along to help.
If you want a single player FF game with a good story, there are plenty of those out there. In fact, XIV's is fairly weak in comparison most of the others (probably because the "protagonist" is a mute idiot who can only nod and do what other people tell them).
Once again, there are dozens of reasons to play an MMO that don't involve the story.
If you saw a player who was a level 50 Blacksmith, for example, who was never seen outside of Ul'dah, hammering away and selling their wares, would you chastise them for not experiencing the story? Would you verbally harass them until they left the game? Would you try to figure out who their retainers are (which is doable) and try to get people on your server to not buy their goods?
When your entire argument is "People have to do it THIS way or it makes me feel bad!", I'm sorry, but you're not even presenting a valid argument.
There is no downside to making the story optional. People can still fight these raid bosses without knowing the story behind them, and they can still pay $15 a month to do it.