Canadian here, so take with a grain of salt. Both Canada and the US don't have a national ID system, at all (short of a passport). A state/province issued driver's license is the default form of ID. If you don't have a driver's license it is very possible you don't have an ID.

Most (if not all?) states and provinces will have some form of "non driving" ID available if needed. However, it is optional, costs money and requires other documentation to get it, such as an original copy of a birth certificate.

It's not that uncommon for an adult to not have an official ID. Either they never had one or have lost theirs and they haven't bothered/can't afford to get a new one.

The argument is that Republicans are exploiting the fact that this will disproportionately affect Democratic voters. Would some Republican voters be turned away? Of course. Would more Democratic voters be turned away than Republicans? Very very likely, and that's the point. It's a net win for one party to enforce voting ID laws while also not supporting some sort of free/cheap universal identity system.