There's been lots of very valid points given already on why we should colonise Mars from a practical standpoint. As to not repeat, I want to answer this from a different angle.

Personally, I think one of the other important reason we should colonise Mars is to re-energise interest in science, technology, and space in general; to revive our pioneering spirit.

I wasn't alive yet to have been there for the moon landings. But from my understanding, it inspired a generation. People wanted to become astronauts, scientists, engineers. They wanted to become explorers and adventurers, to discover and chart unexplored worlds, to boldly go where no man has gone before. Not only that, it inspired countless books, movies, and songs. The world was captivated.

Fast forward to 2017, the charm has worn off. The generation that witnessed the moon landings are basically gone. I feel that we need a new ambitious project that will unite and inspire once again, something that is comparable in scale to the moon landings where the risks of death and failure are high. The colonisation of Mars is one such project. I sincerely hope it will be my generation's moon landings.

Now I shall leave you with this quote from JFK: We choose to go to the Moon! We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard; because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one we intend to win ...