What is wrong with voters bringing some kind of ID to vote?
It disenfranchises people who don't have any officially accepted ID. This is not a class of voter whose distribution is uniform across the political spectrum, so the result is to bias the results in favour of the parties and candidates whose supporters are most likely to have an accepted ID.
This is particularly problematic in the US south, but even in other parts of the country it is mainly black people who are unable to vote as a result of these rules; and the detailed implementation of these rules - which forms of ID are and are not considered acceptable - makes very clear that the unstated purpose is to minimise the vote amongst that section of the population.
Or perhaps it's purely coincidental that the effect of rules imposed just happens to burden black people more than it does whites. Just like it's purely coincidental that there are far fewer voting places in black dominated districts, leading to long lines and suppressed turnout.
It's amazing how many rules that have nothing to do with race turn out to completely coincidentally disfavour blacks in the US. If the people making the rules weren't so quick to assure us that it's all
purely coincidental, it could almost be mistaken for systemic racism.