I agree with most of the people here, the groups you were with were in a rush and because of the 1st set of dungeon's ease ran with it. I've tanked in a few different MMOs, but I didn't even try to do so here until I'd gotten a healer and a dps though every dungeon. At the very least, you could run one of them and a tank at the same time, learning the dungeon on one then tanking it; this would slow down the leveling of both (despite the extra xp the lower leveled class/job would get for being below the other) but gives you the knowledge you need to tank it.
If you state that your new, you should usually get an understanding group. often times, players will do what they can to help you through it; advice (I have a habit of saying FLASH alot to gladiators who can't keep things); minding their own argo/emnity by switching targets if it goes yellow/orange; Running To You instead of Away from you....And making sure you go the right way in a dungeon instead of to that dead end with trash I always end up running towards in some dungeons ;p
I know I've had Black Mages tone themselves down in lower content because my crappy geared tank couldn't keep things off them going full tilt!
Running towards You when they've got things however, only happens about 38% of the time in ANY dungeon run. It's a pet peeve of mine, makes a tank's job easier if its done but you'll have to learn how to pull it off the "Headless Chicken Emnity" Run...Or teach the players not to do so by letting them have it.
It comes down to, Do you Enjoy your Marauder?
If yes, don't give it up because some players are jerks.
