If the story is as underappreciated as you guys say (and I'm not arguing that point, I know plenty people who think the MSQ's cutscenes are tedious and don't watch them), then what will happen if we make MSQ optional? People won't play it.

Why is that bad?

Because like 90% of casual content in the game is unlocked through the MSQ. So now we have new players NOT unlocking these instances, and as older players attrition or lapse sub in between patches, what do the queues look like for 90% of content? It now takes a prohibitive amount of time to get a group. So now even people INTERESTED in the MSQ don't play it because it's to hard to actually get into content. Roulettes (primary source of endgame currency and gear) don't get run because level 50 and 60 content is dead.

Are people going to continue playing for the other 10% of casual content, like PotD? No. It's not a healthy gaming environment. Most of the casual content should be "required" in some way to unlock in order to keep a critical mass of players in the queues and keep content alive.