I agree with LeslieAGD when she says that the decision should be carefully thought out.
Sorry that you are having a bad experience because of some idiots.
Stupid people that ruin an experience for others gets me well

steamed.
Now the first temtation is to do something nasty to them:

But that is a bad idea, the legal repercussions are nasty.
But I understand you are still upset and angry

.
But you want to do is sit back and cold bloodedly consider both the situation and your options.
Friends
Unless the chapter is very small, you probably don't know many of the brothers well. If there are at least 20 plus brothers you don't know well as a pledge, you have a really good chance at bonding with some afetr becoming an active.
Social Place 
Was the chapter honest with you in terms of its social programming and the who they hang out with? If the chapter is pretty low profile on campus you may not want to join it, or you may wan to look at it as a fixer upper.
Pledge Class
I know they seem a lost cause to you, but it sounds like a failure in leadership by both the general chapter and the pledge class. ITs like 50/50 whether a class will be serious and cool, or stupid and lost. And often depends on whether the chapter has some definite guidelines and leads by example through its pledge educators. Or on who takes the initiative in the pledge class. If the wrong people do, the rest of the sheep will often follow and be infected.
Never take your toys and go home
One of the things they tell us as MEN is that we should never lose our tempers and stalk off in some grand gesture. Its really immature. So if you are going to leave, do so, but don't expect them to miss you, like you, or change in anyway when you do.
Anway hopefully we'll know more of what to tell you if you tell us:
How far along in your program you are.
How large the pledge class is.
How large the chapter is.
What the campus Greek system is like, including how many groups.
And anything you think we should know.
Good luck!