That's the point - the One who is sinless took all the sins of humanity upon Himself.
Why was he "alone?" If you are in communion with God, you are with him no matter what, especially if your faith is perfect as Jesus' is believed to be. The "aloness" comes when sin separates you from God's presence, when you feel the Spirit "left." You can't tell me that a man of perfect faith, such as Jesus is known in his humanity, would feel that God had forsaken him unless his faith failed at the last moment.
An interesting argument. Yet, the Mother Teresa types and the OT prophets who were as sinless as men could be (obviously not sinless, but more than such as you and I) often wrote about a gulf between God and themselves, even though their faith was, at least as described, still strong. Did Jesus in His humanity, feel a sundering, if only momentarily at that awful moment? I surely don't know.
No, Mark, if he takes out sins then he is guilty of them (and that's not allowed). If he dies for them, then he is not guilty of them, but innocent, and the Bible clearly prohibits that!