So OP instead of being all “Woe is me” about this let’s try to identify the problem and fix it.
Class- They knew you were a dps warrior when you were invited so this isn’t it.
Spec- This is possible. Are you in a pvp/leveling spec or are you in a raiding spec? If you don’t know the difference then you should look at a few warrior guides online.
Gear- This is the most likely. I think any reasonable person will admit that full pre bis takes some luck (there is always one or two pieces that refuse to drop), but that is no excuse for your gear to be awful. Between badge gear, heroic blues, and craftables a presentable set is easy to obtain with a little effort.
Figure out what the problem is and fix it instead of crying on the forums that nobody is willing to hold your hand.
People act like anyone that isn’t uber casual is an elitist and that just isn’t true. It is not unreasonable for the rest of the people in your raid to expect you to put a little effort into your character. Showing up to a raid in half greens with no gems or enchants is a giant middle finger to everybody else and most will not take kindly to it.