He's not. Listen to his arguments. His worry is that a shutdown will empower the executive even more since in the events of a shutdown the executive gets to decide who to cut from "non-essential" federal workers without any legal recourse.
Schumer worries that causing a shut down might empower the executive more then the proposed spending bill and there is validity to that claim. 

I'm still in favour of shutting down but to characterize Schumer as a traitor is short sighted and naive