Humans are explorers because they are a facet of God, and God is an explorer. The basic nature of God or All That Is is creativity, expansion, unfoldment. As humans, we have this same attribute.
Exploring new horizons gives us the opportunity to know ourselves in a bigger, deeper way. It evolves us. Change, evolution our necessary for our survival.
Given the current events on our planet a new frontier is a good solution to our current problems. It can bring into perspective who we are as humans here on earth, unite us in a common, worthy, exciting goal.
Mars One offers this opportunity by creating a mission to Mars with the intention to create a human settlement.
Here is what the founders have to say.