Why Thanos want to wipe Half of the Universe?

All of u seen the the avengers infinity war trailer,and you want to know that why Thanos want to wipe half of the universe why not full?
So here is the official answer by director of Infinity war-Joe Russo
At a interview given to telegram he said that- He's from a planet called Titan.Many years prior to the film his planet was experiencing a cataclysmic shift.They were running out of resources and they were overpopulated. Thanos made a recommendation that they exterminate half of the population randomly in order to save the rest of population.His notion was rejected and branded him as a mad man,exiled him and the planet end up dying.
So he has taken it upon himself to go planet by planet throughout the universe and wipe out half of population of each planet as a way to correct the planet and bring it to balance.
So by the trailer and movie we think that thanos is villain but from his perspective he is acting as heroic