Most democratic countries either limit or deny altogether voting rights for people with cognitive impairments or mental health conditions. Against this weight of legal and practical exclusion, disability advocacy and developments in international human rights law increasingly push in the direction of full voting rights for people with cognitive impairments. Particularly influential has been the adoption by the UN of the Convention on the Rights of Persons with Disabilities in 2007. Article 29 declares that states must ‘ensure that persons with disabilities can effectively and fully participate in political and public life on an equal basis with others, directly or through freely chosen representatives, including the right and opportunity for persons with disabilities to vote and be elected’. This article also argues for the right of all people to vote, including people with cognitive impairments, by adopting a uniquely strategic approach. Firstly, some of the strategic limitations of existing arguments in favour of extending the franchise are highlighted. Most such arguments are flawed because they run the risk of inviting disparaging philosophical commentary which compares disabled people to animals, or because they are based on implausible empirical claims, or because they inadvertently tie the case for voting rights for the disabled to other cases unlikely to ever enjoy widespread acceptance. This article, instead, justifies extending voting rights to all people with cognitive impairments based on a simple cost-benefit analysis that avoids all of these problems.