If someone wanted to argue that Tom Robinson is freer dead than alive, then he or she could say a few things.
First, Tom as a dead man does not have to suffer in a world where white people have power over black people. His trial shows that no matter how innocent you are, it does not matter where whites have control. So, even if he lived, his life would not be free.
Second, as a dead man he does not have to see his family suffer. It is clear from the church scene where the church is trying to raise money that the Robinson family does not have enough money.
Third, we can say that Tom would be spared the thought of his family worrying about him in prison. Now that he is dead, perhaps his family could move on.
Finally, as a Christian we can say that Tom is in heaven. His family would have certainly believed in this.
All of these points show that death makes Tom freer.