Painless executions are easy but immoral

I oppose capital punishment.

But it surprises me that states are struggling to find ways to execute people painlessly.

There are two easy ways to kill people painlessly.

The first is carbon monoxide. People often die in their beds from carbon monoxide poisoning (due to improper ventilation of a heater, for example). They feel drowsy or sick and nod off.

Someone suggested that because the Nazis murdered people with CO, its use is unacceptable. That argument doesn’t seem convincing.

The second way is morphine.  Some people might oppose that method because the criminals would live their last moments in bliss, and that would defeat the vindictiveness of many people who want to punish the criminals.

I certainly don’t want states to use either method. But they seem more humane than firing squad, hanging, lethal injection, or a gas chamber.

Why don’t states use carbon monoxide or morphine?