In Slytherin go all the wizards and witches who have a bit of evil, who can become Death Eaters and who have are clean blood or half blood.
It was created by Slitherin Salazar who left two things at Hogwarts: his necklace (became a horcrux) and the secret chamber for cleaning the school of Muggle-born witch wizards.
If you are from Slytherin you can feel more majestic and just because you are from this house does not mean that you are Death Eater.