I think that Salazar Slytherin was justified in wanting to keep Hogwarts open to only the students who came from pure-blood families. They were living in a time of persecution from Muggles. That being said, Salazar Slytherin then creating the Chamber of Secrets, keeping the Basilisk which was to be used as a revenge against Muggle born students in wholly unacceptable. The original fear was reasonable, his reaction was not.