"... 'How can a man who is a sinner perform such signs?' ..." -- John 9:16
This is a worldview question. If God alone has the power to heal, then only those in harmony with God can heal and only by his authority. Sin is rebellion toward God. The sinner cannot heal because he is out of relationship with God and therefore can not act by his authority. Jesus heals so Jesus must be in good relationship with God. But he breaks the Sabbath. Therefore he is a sinner. Therefore he is out of fellowship with God. Therefore he should not be able to heal. But he heals.
"'... We know that God does not hear sinners; but if anyone is God-fearing, and does His will, He hears him. Since the beginning of time it has never been heard that anyone opened the eyes of a person born blind. If this man were not from God, he could do nothing." -- John 9:31-33
We don't have this problem, though we ought to. We have the problem that we attribute healing to agents other than God. God doesn't appear in our worldview because we've convinced ourselves that he didn't create the universe. Instead, the universe created itself. With God out of the picture, so to speak, we need then to identify what agents bring about positive change. We see man as the healer, medicine as the healer, science as the healer. We see man doing amazing things so we glorify man and his knowledge. Only when a limit is reached is there a sudden reaching out for God. Sometimes he permits himself to be found. Other times not.
And we, like the Pharisees, say "we see" (v41) and yet we are utterly blind to ultimate reality. And so our sin remains.
Would that we were able to see God as he really is, and the universe as it really is. But instead, we are deaf, blind and mute. We do not hear the still small voice of God. We do not see his hand in all things. And so we are unable to speak of his glory. We are crippled, crippled beyond all measure.