I agree that violent felons have shown below-average decision making capability, but as much as I don't necessarily want them having a voice in running the country, whether there are costs to not letting them do so seems to be at least an open question. There is a significant negative correlation between voting and recidivism (http://www.allacademic.com/meta/p_mla_apa_research_citation/...), though it's easy to see how the causation could run mostly in the opposite direction.