Interesting topic. For a truly balanced view, I recommend people on both sides of the isle watch this TED speech from Jonathan Haidt. It's mostly aimed towards liberals that have a set preconceived notion towards conservatives, but I suggest that people on both sides of the isle watch it.
http://www.ted.com/talks/jonathan_haidt_on_the_moral_mind.html
The gist of it is that people like to think that "the other side" is stupid and irrational, but the fact of the matter is that both sides contribute to society and share common moral values.
My personal take on it is that conservatives are important in that they keep the traditions and are keepers of knowledge, transferring these traditions and knowledge through the generations and keeping them alive. Without conservatives in the mix, liberals would go too far and spin society out of control until it became a state of anarchy.
On the other hand, liberals are important in that they stress the edges of what society is capable of, slowly expanding the boundries of what it means to be human. Without liberals, new ideas wouldn't proliferate and gain momentum in terms of societal standards, so they are necessary as well.
In the end, think of it as the properties of a good sword. A sword that maintains strength, yet is flexible, is the ideal hand to hand weapon. A sword that is too hard (brittle) is prone to shattering, and a sword that is too flexible doesn't have enough strength to do damage. It is only by having the proper mix in the steel that makes the sword that it becomes an ideal weapon. In this analogy, the liberals are the bendable property, and the conservatives are the hardening property.
In that manner, a nation state can fail if it's too bendable / soft, precisely because of the overbalance of liberalism, allowing them to be an easy target to be taken over by other nation states. If the nation state is too hard (ie brittle and filled with conservatives), it doesn't grow and the citizens are miserable (look at North Korea as a prime example, or Afghanistan). It is only by having a proper mix of liberal and conservative citizens that a nation can be truly strong.
In the end, walking a line of balance is always the most difficult path; it's easy to be completely on one side or the other, in other words a black and white mentality. The more difficult path of a balanced approach, however, yields much better returns in the end, as it does with most things in life (for example eating too much food makes you fat, eating too little makes you weak). To walk the line of balance requires one to put yourself in the shoes of both sides, and it is only thus that the balance of humanity is maintained.