Why did persus kill Medusa?

Answer 1

Sure did! Cut her head off and walk around (sometimes flew with his winged sandals) with it in his bag. Kind of gruesome but that's the way the old-folks were like in those days.

Oh you asked Why! His soon to be step-father Polydectes didn't like him and sought to get rid of him by sending him on an impossible task. So when the time came for presents Perseus offered his services, (the present of the day were horses but being employed as a fisherman Perseus had no horse to give.)

And Polydectes asked for the head of Medusa.

And being the brash young man that he was Perseus accepted even thought he had no idea how he was going to accomplish such a deed.

Now the story on Medusa is kind of complex. She was the center of a controversy that involved Poseidon (one of the big three of the Olympians). The Olympians wanted to put Medusa out of her misery and retrieve the 'dangerous' articles of power that Athena had (in a rage) bestowed upon her as a curse but to do so would be to incur the wrath of Poseidon.

So the Gods (including Zeus) stayed out of it.

But then along comes Perseus and the Gods thought they saw a chance working through him. Athena gave him a shiny shield and a means to accomplish his task. Hermes gave him the winged sandals so he could get around the great distances involved. And Hades (the real power behind the operation, another one of the big three Olympians) gave Perseus the Helm of Darkness.