I belive around the time when Sly and the other founders were at hogwarts muggles were takeing magic badly

Of course he did. He wanted to exclude Muggle-borns from the school and he built the Chamber of Secrets specifically to purge the school of them.

@simpleplan, The Muggles weren't bad at magic- he simply didn't trust them because previously wizards had been persecuted by Muggles. He held them all responsible even though obviously not every single Muggle played a part in the persecution.

I think so because at the beginning of when Hogwarts was open they said Slytherins were mainly of the purest blood and that's why he left, because too many half-bloods and mudbloods were being let into the school as students, and mabye staff.

Salazar Slytherin was always crazy about blood purity. He was the one who wanted only purebloods.

Absolutely! It was the ONE thing that differentiated Salizar Slytherin from the other wizards and witches that founded Hogwarts. It was this exact topic that he had a heated argument with Godric Gryffindor and then left Hogwarts shortly thereafter. Gryffindor believed anyone with magical powers should be allowed to attend.

Salazar Slytherin himself was the one that thought only Purebloods were the only ones worthy enough to study magic.

Yes. Because if you look in the Order of the Pheonix, and at the sorting hat song, it says so. It says excatly, "Said Slytherin, 'We'll teach just those whose ancestry is purest.'"

No, I think he wanted like an aristocracy of pure-bloods, but not that every wizard were pure-blood

He started the whole pure-blood supremacy idea.