Voter ID law upheld

In a blow to Democratic opponents of state's efforts to enact voter ID laws, the Supreme Court upheld a voter ID law out of Indiana. Probably because of a glaring legal problem:

But the Democrats who sued to block Indiana's law in 2005 did not name a single plaintiff who had been barred from voting because of the law. And that failure doomed the legal challenge.

I'm no lawyer, but from how I understand lawsuits to work, someone has to have something to complain about that's actually happened, right?

It is a bit confusing, though, that at least one Justice seems to have no problem excusing the partisan roots of the law:

Stevens acknowledged the Indiana law may well have been "motivated by partisan concerns," but that alone is not enough to make it unconstitutional, he said. The challengers failed to show the voter ID requirement would pose a "severe burden" on many voters, he said.

That alone? Well, if you can point to it as a motivation, shouldn't that lead you to potential harm? How confusing.