Dave Nalle analyzes independent voters:
Independent voters want to protect their interests and protect their rights. They know that the activist extremes of the two major parties have agendas which involve whittling away their rights in all sorts of areas, in service of religious, moral and political ideologies. They also understand that the parties have to cater to these extremes in order to turn out reliable, core votes. But above all, they have a simple agenda of their own. They want to be left alone and to protect their families, their property and their wallets. In picking how they will vote independents have to decide which party's extreme agitators are more threatening to them.
This is where the Republicans tend to win out. While the radicals of both parties want to limit liberty and impose intrusive restrictions on people to further their marginal causes, the general threat level of the Republican extremists is more acceptable, however reprehensible their specific issue positions may be. Most of the ways that extreme Republican factions want to persecute people and take away their rights apply primarily to small groups who are relatively politically unpopular and to rights which many people see as being of secondary importance. In contrast, the radical elements of the Democratic party tend to promote policies which impact very fundamental rights and which would affect much larger portions of the population. In grade-school terms, the Republicans are like playground bullies who are going to take lunch money away from the whiney unpopular child who picks his nose in class, while the Democrats are the crusading parent who wants to ban recess for everyone because someone could get hurt on the playground.
The main bugaboo of the Republican party is the religious right. They're mostly out to get homosexuals and to ban abortion. Both of these issues target relatively small and unpopular segments of the population. Homosexuals are everywhere, but they're less than 10% of the population and they're out of the mainstream by definition. They are seen as alien, threatening and objects of derision by a lot of people, even though they may know better. Everyone knows that unplanned pregnancies are a problem, but underlying the surface sympathy is a resentment of the mother and a condemnation of the presumed promiscuousness which created the situation. Again, women seeking abortions are a small and powerless group and one which doesn't evoke a lot of genuine sympathy. In both of these examples most independent voters can easily say "what do I care, I'm not gay and I'm not going to get knocked up with an unwanted baby."
The same holds true with the issues of the extreme 'law and order' Republicans. Most people don't plan to commit a murder so they don't mind the death penalty. Most look down on drug users so they put up with the War on Drugs. Most can even look at infringements of privacy rights under the 4th Amendment and not worry because they aren't criminals or terrorists and therefore have nothing to hide. Restrictions on social service programs are an acceptable evil because those people should work harder and provide for thesmelves. This attitude even extends to some degree to situations like the War in Iraq. It mostly afflicts people in a foreign country, and a very small number of US soldiers who volunteered to be there in the first place. In all these cases the independent, self-centered voter can frown and say "What does it matter to me? I'm not really directly hurt by any of this."
The independent voter may not like any of these programs. They may be nominally pro-gay and pro-choice and anti-war and pro-drugs, etc. But when it comes down to making a choice most of them ultimately decide that if it doesn't hurt them directly it's an acceptable compromise.
In contrast, the more radical elements of the democratic party promote policies which independent voters find much more generally threatening. These are generally political objectives which go against the three most basic rights of life, liberty and property and which apply to the majority of people in the society.