I wouldn't get bent out of shape by what folks in Dungeon Finder have to say. They have a tendency to be touchy as it's a mish-mash of differing loot priorities, reasons for being there in the first place (I go in for Valor Points, others are going in to gear up alts), and people who are honestly there just to troll.
Always remember that while you should put forth your best effort to cooperate with the other 4 people who are in your group, you aren't there for them. You don't require their permission to do a single thing on your character. You don't require their permission to roll on gear with the priorities you choose, you don't require their permission to use any given spec in "regular" or creative ways, you don't require their permission for anything, and I'm on an active campaign to alter legacy player thinking which says a player does require their party's permission for things.
Usually it's people who haven't sufficiently altered their thinking to accommodate the new paradigm Dungeon Finder has brought about. Before cross-realm groups, people had to form groups from same-realm populations, and had to court reputation carefully in order to maximize the available pool of players to form groups with. While I think it's important on a broader level to behave sensibly in Dungeon or Raid Finder groups (just because I like trying to be a friendly person), the reality is cross-realm groups where you're thrown in with up to 4 or 24 other strangers has a different social dynamic. Letting them force you to do something you don't want to do only benefits them; you don't get the benefit of their good will over the long haul, and thus have no particular incentive to change the way you choose to play your character that you pay the subscription fee for.
Go into Dungeon Finder, be considerate, put forth your best effort for the role you chose when you queued. Roll on upgrades for either of your specs as you feel personally appropriate, and ignore people who try to make you do things their way. The worst that can happen is you're booted by someone looking to abuse the Vote Kick system, and there are tons of other things to do for 30 minutes while that debuff ticks off. Then re-queue.
Most of the time you aren't going to be kicked. Most of the time people remain quiet and just get the dungeon finished. This is, I think, how it should be, though some fun conversation as appropriate (I always try to remember that a lot of people don't type as fast as I do) is optimal.
Get in, get points/gear, ignore the jerks (really /ignore them, so the system doesn't group you with them again), get out. That's the way Dungeon Finder works.