Any electoral fraud that relies on having bunches of people vote multiple times necessarily relies on there being a conspiracy of >100 people in order for it to be effective (this is the only kind of fraud that can be prevented by demanding that voters produce photo ID). But if a conspiracy is required, then why not address that directly? Offer a $500,000 reward and immunity to any one who provides information about…
How does vote fraud necessarily rely on a conspiracy? In many states, knowing someone's name and address is sufficient to vote as that person as long as they've previously registered. Any individual can show up at the polling place multiple times and vote as someone else and it would be very difficult to prove they'd done so.
It really doesn't make sense spending money to prevent attacks that are completely economically infeasible.
Besides, let's say we require ID for voting. Now, everyone who illegally voted before can continue illegally voting: all they have to do is get some fake IDs, which any bored teenager looking for beer can do.