Because that is how our political system works plain and simple. We have political parties they are how you influence power in this country. We need to be realistic and quite frankly not foolish, there are good people in the Democratic and Republican parties and there are bad. What is really bad is what this mechanism has done to the people and there views clumping it into two parties. I am a gay marriage loving, gun toting, universal health care, former worker at a defense contract PERSON.
This is what i feel is so crucial: When elections come around, I do a lot of reading, watching, listening, and talking and I decide which candidate from all of the political parties best suit my ideals. In 2008 I had a really hard time deciding between Bob Barr (libertarian) and Baruch Obama (democrat) because a lot of there views are similar.
In the end I voted for Baruch Obama because a lot of libertarians, including Bob Barr don't put spending on social services like medicare, medicaid, food stamps very high on there budget, and in fact sometimes with more intense libertarians not at all (which turned me away from there party, its a very selfish party)
This keen observation of peoples policies and stances beyond just Pro-Choice or Anti-Choice and polarized subjects like that is vital to breaking the cycle of a two party system. Get away from the "well *** that guy, so ill vote for this guy" mentality, its ignorant and dangerous.
Not to mention its not necessarily a middle path I think the VAST majority of the people here are fairly "left" leaning on social issues. Its adopting what from both parties you find acceptable. If conservatives REALLY believed in conservative government they wouldn't be trying to decide who can and cant be married. They started before Ronald Reagan and Dwight Eishenhower as being a small less spendy and less obtrusive government but tossed those values aside to "Fight the commies" and win the votes of those extremely hyperbolized voters that thought Democrats where "ruining America".
"Party spirit is a lying, vociferous, reckless spirit, a stranger to candor, willing to pervert the truth, and to use underhanded and dishonest means so it may gain the victory"
-Charles Simmons 1798-1856 (Said in 1830s)