The voter ID law in Wisconsin disqualified 9% of its registered voters. The right to vote is protected by 5 constitutional amendments and isn't conditional upon obtaining a state-issued photo ID. Requiring a photo ID is akin to a poll tax (24th amendment). There's no evidence that photo IDs make elections more secure, since voter-impersonation fraud is practically non-existent [0].
[0] http://www.latimes.com/business/hiltzik/la-fi-mh-why-voter-i...