The only argument I find valid is the third.

I don't personally see how it gives the law too much power.

I'm sure it's morally questionable, but that isn't really a good reason by itself, is it? Abortion is morally questionable, yet I know you support it, at least to a degree.

I do agree that the possibility of killing innocent people is a huge downside. However, I wouldn't say that it's actually impossible to tell whether or not someone is guilty, though very difficult.

All but one of your major arguments are about how the death sentence does not help, as opposed to why it should not be used, so for right now I'm just sticking with this.

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"True wisdom comes to each of us when we realize how little we understand about life, ourselves, and the world around us." ~Socrates