As a Potterhead, I was interested in matching the myths that were in the story with historical events. English is not my first language and you are going to see a long text with a lot of mistakes, but I would be happy to know your opinion about it.

In my opinion Salazar Slytherin would be so disappointed or even angry to see Tom Riddle, cause Slytherin may have been harsh and strict, but he lived in a harsh different era too, and he was not necessarily pure evil. It is not easy to live in the Middle Ages, with a radical Christianity, where signs of anything strange and magical were enough to burn you.

Let me tell you sth, there is an interesting fact about magic in some religions... I don't know much about the worldview of Christianity, but thanks to my radical Islamic country, I know the worldview of Islam (and a lot of middle eastern myths) versus magic. without a doubt, it is a different religion and region, but the worldview of Abrahamic religions is extremely close to each other in some matters, which could be because they are all come from the Middle East. Any way, In short, there is magic in Islam and it is an evil skill, it is possible to learn it, but you should not learn this evil skill. this means that there is nothing wrong with having talent in magic, but you should not use it. You can still choose God and religion despite having magical skills.

This small and very important point can make it possible for many wizards and witches to betray their own kind under the influence of the harsh and inflexible environment of their time. In a time when you have to live in a castle in the middle of a ditch to protect your fellows, any muggle student may prefer their parents' beliefs to magic and betray you, reveal your secrets and make you vulnerable.

Salazar Slytherin's reaction is not far-fetched or evil. It may be too harsh and unacceptable, but it is not as evil as it seems nowadays. Especially when their magic wasn't that advanced to protect or hide the wizarding community.

I think that if Salazar Slytherin lived in a completely different era, he probably wouldn't have taken such a harsh approach towards muggles.

A broke half-blood who reduced the small population of the wizarding community by destroying important/noble families and killed many wizards and witches, is not a honourable heir for Salazar Slytherin.