Yes, that is something Trinitarians don't understand. It is dangerous to assign sin to God in any way, shape, or form. I also believe it's pardonable because many people are just genuinely misunderstanding the Bible on the point of Jesus becoming sin.
The doctrine of the Trinity is not precise, more like performing theological surgery with a chainsaw rather than a very fine scalpel. They created the form of their beliefs, but it's very rough around the edges. Things like God becoming sin, God dying, etc are questions they have not accounted for.