The outsiders
do they really have no choice to be greasers?

Yeah, it's really not up to them.  

Explanation:

Their "rank" was decided on where they were born and what they looked like.   Greasers were normally born into poor communities (not necessarily money wise, but behavior wise).  To be a Soc, you really had to be born with a lot of money and the freedom to kinda do whatever you want.  There was no way this split would ever dissolve either.  It would always be something that seperated the rich and the poor,  The wealthy and the unfortunate, etc.  

sorry, but there are no bolded