I agree with you to some extent, but the problem is that the political parties have decades of experience with the current winner-takes-all model. If we were to

I agree with you to some extent, but the problem is that the political parties have decades of experience with the current winner-takes-all model. If we were to move to a model where they have to share power and cooperate they would have to completely rethink the way the parties market themselves to the electorate. At the moment they write a manifesto, and people expect them to deliver on what the manifesto says if they get in. With a coalition no party can guarantee that, so the manifesto loses its value. The criticism that the Liberal Democrats ran in to demonstrates the problem: they campaigned for proportional representation, which I believe would be more likely to deliver coalition governments, and even on their most optimistic days I don't think they would believe they could gain a parliamentary majority. Knowing that, publicly signing a pledge around student tuition fees was hopelessly naive, as there was no way they could ever guarantee they would deliver on their pledge. And if the Lib Dems haven't worked out how to market themselves in a coalition government, you can guarantee the two main parties won't have done.