It certainly is if
You've removed my pivotal question in your quote and replied to something much less meaningful. I'm happy to have an interesting discussion if you want to continue, because I think it's an interesting subject and not because I have an agenda to push (because frankly nothing we say here is going to impact existing policy either way) but that conversation is going to be much less interesting if we're answering half-questions.
You made a bold statement that said (and I'm paraphrasing) that because an innocent person could be put to death that no people should be put to death. I'm not agreeing nor disagreeing with that statement, but I'm asking if it's really any different than saying that because an innocent person could spend their entire life in deplorable jail conditions that no person should be put in jail? The burden of proof is higher in a capital case so how does one justify innocent people spending life in prison while at the same time condemning execution?
I'm not 100% convinced that letting an innocent person sit in jail for 60 years is any different, and many would argue is worse, than dying. If that is true then what makes us think that incarceration is morally superior to execution? Irreparable mistakes will be made either way.
As for the guilty, doesn't worry me a bit. As long as they don't get out, society has been equally improved.
Has it really been "equally improved"? Or would the $1.5 million dollars ($30k/year for 50 years) it costs to incarcerate that person for life have a greater social benefit spent in reducing future crime such early childhood education, community outreach programs and mental heath? Further for those that are released after murder, rape, etc, after x years and re-enter the society as their "debt paid" and then re-offend, what is the cost to that, both financially as well as impact to social improvement?
A quick (and horrifying from current social acceptance) math exercise shows that executing the 159,000 people serving life sentences (in US prisons as of 2012) would provide roughly $5 billion dollars a year (or a quarter of a trillion dollars over the period of time those people are serving their sentences) that could be directed to social welfare. If there is one thing we do not have a shortage of on this planet, it's people.
This is like trying to say that because some people die in traffic accidents, it's ok if your kid drowned in the neighbor's pool with no fence. The one has NOTHING to do with the other.
The point I was trying to make was that with any policy there is going to be mistakes, whether those mistakes are in execution, or whether the mistake is in non-execution - those mistakes are going to cause innocent people to die either way.