Why did Goku leave with shenron?

Ever since goku arrived evil existed. The andriods, cell, raditz, vegeta, freiza and others that dared to challenge goku. He left with shenron so that evil will never set foot on earth. Goku made the assumption that it was his presence that caused harm to earth. Thereby making a noble decision as he always does, he decides to leave the earth. The dragonballs entering his body means that he is kind of the guardian of the earth now. He is somewhat a godly figure.