1. Some criminals would be more likely to fear a life in prison than to be executed. That would be more of a punishment since many of them already are willing to take their life after what they had done. For common people, the fear of death could stop them from committing a crime, but for someone who has a serious issue and kills someone intentionally (usually the ones on death row), will not stop before they actually kill someone only to change their mind due to a fear of dying. It likely won’t even cross their mind.
2. If someone is wrongly convicted, we could be killing innocent people. These cases are often so complex that it is difficult to find evidence to prove that someone is truly innocent. The government should not be able to kill innocent people even if they thought they had been criminals.