Why can't we debate things like intelligent respectful human beings?

I'm from England and I live in America, and I just spent three weeks in England before coming here to Germany for a study abroad trip. And I'm at an American university in Florida so my other classmates on the trip are American. I've lived in Florida 5 years so I'm pretty used to Americans/able to communicate and I'm used to conservative political views, but there are still things that make me crazy.

So I just want to know, why are some americans so conservative and unable to understand/listen to other oppinions?

We somehow got onto politics and this girl whos super awesome/nice happens to be really conservative, so she was talking about it, and how obamas socialist. And I was trying to explain that liberalism/socialism is on different scales in America and Europe/UK. And that the reason there are different policies in europe comes from different views towards society and the role of government. But she had to go the attack and not discuss this with an open mind but just revert to attacking. I wasn't even trying to defend liberalism, I was just trying to explain why the UK has a health care system and why Obama wants to implement a similar system. But then she got on this rant about why that sort of system is unfair and wouldn't work, and that's why communism would never work. But I wasn't even talking about communism. That's why I hate politics and I get out of touch and don't listen to it, but seeing what's going on in England and watching the news makes me realize it is important to know about and keep up with, its just so frustrating that there is no discussion and respect. I wasn't trying to force my opinions on her, they aren't even my opinions, I was just trying to show her a different perspective, and she just jumped down my throat about it.

I love people regardless of their political views, and conservative opinions are just as valid as any other, I just wish we could have more of a conversation instead of feeling like I'm talking to a brick wall.