In that case, I fully agree with you. That is the exact reason why the death penalty is still used in the countries that use it the most. This country is the sixth highest, "only" executing 39 people in 2013.
We're behind Saudi Arabia (79 the same year, despite a much lower population), Iraq (at least 169, despite an even lower population), Iran (369, starting to see a trend?), North Korea (they don't release their records, but it's believed to be thousands), and China (they also don't release records, but the estimate is 2,400 official executions, key word there is "official").
The three countries below us are Somalia, Sudan, and Yemen, three places we also aren't exactly friendly with, who I doubt have justice and deterrent in mind when they do it.
This should tell you something.