Why do we want to go to other planets?

I see talk every know and then about visiting and even setting up permanent habitats on the moon or mars ...why?I just can't see a purpose, it's not if we can live there easily...the environment is way harsher than any other place on the earth amd not suitable for growing food...it's easier to live in the arctic than on the moon or mars. so what is the deal. If it's for exploration then why don't we just send robots...surely that would be much cheaper