Well, we get into the philosophical definition of what "their own interests" are.

But in general - the statement that "people do not vote unselfishly or in a way they believe reflects the community" is false. It is true that some do. I've read some research before from western countries that have a multiparty system (UK, Germany, France, Israel, ...) and with very high probability, people vote for whoever it is their parents do. It's not national interests - it's familial interests and/or identity. (And, sorry, I can't find a link to that right now)