Great question. But yes we can blame Judas – we cannot condemn Judas. But we can blame him for his choice.
Choosing to betray Jesus was a free-will act on the part of Judas. He could have chosen not to betray Christ. Remember that we humans think linearly and God, being omnipresent, omnipotent and omniscient, sees everything outside of time and space, which are both His creations.
Judas was not destined definitively to betray Christ. In fact every grace was given to him so as not to betray and later to repent and seek forgiveness. Check out St. Peter who pretty much did the second worse thing to betraying Jesus, he denied Christ 3 times. Jesus warned him that he would and even when he saw himself doing it, recalling Jesus' words – St. Peter did it anyway. The difference is that Peter was repentant and sought forgiveness afterward.