ELI5: Why do so many people oppose requiring IDs for voters?

So, I'm left of center... but I don't understand why so many people, mostly liberals, oppose requiring IDs for voters. I've heard that this is, somehow, a strategy to suppress minority or poor voters. Is it commonly accepted that most minorities do not have state IDs? If so, why is this the case?

edit: Thanks for the replies. I hadn't really considered the difficulty that some people might have in obtaining an ID. My driver's license IS my state ID, and so I've had one since I was 16 and I hadn't thought about people for whom this isn't the case.