There are several reasons why political discussions has broken down. But I will just mention one.
I believe it comes down to people no longer having a philosophy of their own or a traditional set of values they can base their lives upon.
First let me address the philosophy aspect.
People nowadays hate to think. They want simple solutions to life, and hate the anxiety that comes with accepting uncertainties in life. They want the answers to life handed to them on a silver plate, and do not want to go through the painful process of tearing down old values and raising up new ones. This is why many have given up any serious intellectual inquiry, and regurgitate information others feed them. However, critical thinking is more necessary than ever due to the bombardment of misinformation over the web and the takeover of the academia by corporations.
Now, the value aspect.
Without a philosophy of your own, you would at least need a set of values you could orient yourself with, which have been instilled in you by your parents or by your community.
The problem however is that this current generation has been taught to rebel against anything their parents stood for, and that they should ultimately strive to be "free." But what does it mean to be truly free? Does having the money to drive a BMW, living together with your girlfriend without marrying her, or taking trips around the world each year make you truly free?
I believe that people are so obsessed with just running away from their responsibilities, that they have never truly considered what it means to be free and what they are running away to. If you think for a moment, what limits our freedom is not so much our obligation to our families or our old beat-up Ford, but the spread of neofeudalism around the world today, as the gap between the rich and poor widen and laws are applied differently to the rich. In all honesty, does that trip to the Bahamas really make you free?
This breakdown of family and community values is aggravated by the fact that corporations are moving jobs abroad, which results in the uprooting and destruction of entire communities. Even for the suburban middle-class, more moms and dads are finding that they both have to work to make ends meet, which leaves the question - "Who is going to take care of little Johnny?" "Who is going to take the time to instill him the right set of values?" Families are seeing less of each other, and communication breakdowns become more frequent, as any relationship requires time and effort for it to work.
But how can you count on anyone to treat others with respect, if he cannot even treat his own family members with respect?
So where does that leave us?
It's simple really. Without a philosophy or a set of values in our lives, we are no longer different from the animals. We are driven by power, greed, or whatever happens to hit the spot at that moment. It shows even in small things, like online debates, where people won't ever admit that they're wrong, and try to learn from others. We believe ourselves to be rational creatures, but when you face the reality, we are often driven by the same crude instincts as the animals who know of no such things as compassion or love. It is only our philosophy and values that makes us human.