Why do democrats think poor people and old people are stupid?

We are passing a law in wisconsin that has people show a form of ID before voting. I don't know that it is necessary, but if it prevents a few unregistered voters from casting a ballot i guess it's not all bad. The democrats are exploding though. They keep saying it will make it harder for immigrants, senior citizens , and low income people to vote. I don't get the argument. I don't see how age, country of birth, or financial status affects your ability to carry your ID. If you want to argue that it violates your liberty, well I think it's a stretch, but we could have that conversation. But to say it somehow affects certain people differently seems crazy. Can anyone decipher this liberal mumbo-jumbo into something that makes sense?