First of all I haven’t played Tera, but it sounds like your generic groupfinder; you enter a queue (with a certain role in some games) end up with 3-7 other people, do the dungeon, if I’m completely misunderstanding, my apologies and stop reading.
The current groupfinder usually shows a majority of people asking for people who stack, even if non-zerkers are welcome. If you play zerker, you know many non-zerkers still try to get into zerker groups. You know what this means; the majority prefer getting things done quickly and efficiently.
So you introduce your random groupfinder, there will still be a majority of people who will want to stack or follow some kind of tactic to make encounters easier. On top of that you’ll have some people that don’t mind either way (new players for example) and adjust to whatever works best (stacking most likely) and the players who don’t want to stack will stay the minority and will be forced to adjust on their group if they have any sense of democracy.
Before you know it, everyone who completely loathes stacking will stop entering the groupfinder and those who prefer not to, but rather do the dungeon nonetheless will stop trying suggesting other ways and just go to the stacking corner without saying a word.
If you don’t want to stack, make your own post and show some patience. It’s in most people’s nature to want to get things done quickly, even if they do enjoy what they’re doing. But you will find people joining you, new players and level 80s alike and you’ll have a blast. Whenever I’m leveling with a friend (or help them leveling since I’m getting too many duplicate professions for no reason) I make a groupfinder post along the lines: “Warning: new players, anyone welcome” and I add things such as ‘no stacking’ if desired by my friend(s.) It’s not instant like my “Lvl 80, zerker only, class X and Y only” posts, but it does get filled, eventually.
You’d be surprised with the people you meet. I’ve met a lovely fellow who invited us to his TS and started chatting with me and my friends, turned out he was a zerker even though they preferred to play without as stated in our groupfinder, so he and I decided to just take some pieces of armor off to slow down the run for them. (I’m sure if this was after the first feature pack we’d respec aswell.) Met loads of lovely new people who were incredibly happy with all new information my experience provided and loved a little link towards dungeon mentors. Met veteran zerkers who just enjoyed the change of pace and discovered new things aswell, also shocked by the challange it can present.