I really doubt that tons of people would join dungeons, switch to a crafting class, and be a big useless troll. That's just the same as going AFK in a dungeon now and I don't see that happening outside certain endgame things where they want to be carried (and measures will be taken against that BS soon, I'm sure.)
Anyway, if you're concerned about them changing classes, maybe they could implement a repair for dungeons where you just change to your crafting class automatically when you click repair on an item, and then it automatically switches you back to your combat class right away after the item is repaired. Thus you aren't out of your combat class for more than a second. Problem solved
Right, right, you should always be prepared and all that. But we're human, if people end up making a mistake and forgetting to check all their equipment ahead of time, which will always inevitably happen somewhere to some group, does that really have to ruin the dungeon run for everyone?
So many people are complaining about how bad the community is, and how awful DF groups are. Part of the reason for this is that tiny, reasonable mistakes that tons of people make can ruin the whole dungeon run, because FFXIV makes their dungeons less convenient than other MMOs. Why would you be against them making DFs a little more convenient in a way that makes sense???
Allowing for a few mistakes like this in dungeons make DF groups less frustrating, and doesn't make the gameplay easier or anything.
Seriously, a slippery slope argument? >_>
It doesn't make any sense to be able to buy stuff when you're in a dungeon, but it does make sense that you can repair your equipment if you have the crafting class leveled and the dark matter with you.
Are you all so desperately against convenience and good quality-of-life mechanics that make the community happier?