Because they tell us to. Because if we can get worked up to believe that the opposition represents an affront to our most cherished beliefs and that their policies are "evil," we will get worked up enough to put the other side into power, which is exactly what they want. We can do their fighting for them. If we can blame "the other side" for all of our problems, we feel like we have an enemy we can defeat. If only things were that easy.
We aren't as different as politicians would have us believe. Heroes and villains sit on both sides of the political aisle, and have throughout history. Most of that posturing is their fight, not ours. On top of that, no one person elected can fix or change everything. Lincoln alone did not end slavery, that was a long-fought group effort. Civil rights and women's rights were fought and won because groups of people came together and worked for change, not because one person or one political party made it happen, no matter who sat in the Oval Office at the time.
I'm not going to deny that certain issues are important to me and that I will fight for them. I'm not going to deny that crazy people run for office and get elected on both sides, or that there are candidates that I support in full. I just get disheartened when people claim that they have lost faith in the entire country or in all of humanity because of the outcome of one race. We are greater than that.
We vote for more than a President. The President can't act alone. Your vote yesterday mattered for so many reasons. Senators, congresspeople, DAs, council members, state and local issues... your vote does not stop at the top and it may even speak more loudly the bottom. Nor does your ability to affect change end when the voting booths come down. If you want change and feel strongly about it, don't wait for some figurehead to do what you hope they will, go work to make it happen. Work with people instead of against them. Put party labels aside and don't resort to name calling or violence. Change starts with you. Run for office. Volunteer. Write. Do whatever you can to fight for what is important to you. It matters.
Not only that, there is so much more to life than political bickering. Take a break from fighting and arguing about abstract ideals and issues and appreciate the life and people around you.
We won't be here forever.