While it is clear that the United States has an unusually low voter turnout (see the PBS article below for statistics and analysis), there is no generally accepted theory on why this should be so. One theory is that the costs of voting outweigh the benefits for an individual. It is almost inconceivable that a single vote will make a vital difference, but, in order to vote, the citizen must take time out of a busy day and, even before doing this, inform himself/herself about the candidates and issues.
One consequence of low voter turnout is that representatives do not necessarily reflect the will of the people. They will be much more eager to further the interests of the groups who voted for them and are likely to do so again than to represent the politically apathetic. Another consequence is that voters become even more skeptical about the democratic process.
Whether or not you are in favor of voter ID laws, you should bear in mind the fact that these laws reduce already low voter turnout still further and may discriminate against low-income voters who do not have passports or driver's licenses.