Saudi is an ally because of convenience. They sort of help protect Israel. They fight back Iran. And they give us access to the Golf. They are also very friendly to our defense vendors, buying all sorts of weapons at good prices.
You could argue that these reasons are not good enough. You could argue that they teach forms of Islam that hates America. You could argue that they hate Israel too. And I would not disagree. But our state department chooses to take sides in the Iran, Saudi feud. They do this to keep Russia on one side and us on the other. They do this to keep Israel around as well as Jordan and Egypt. It may be a pact with the devil but its been around since world war two.
This is why I despise what foreign policy has done to our nation. It's a "choosing a devil who serves you" argument. Devils don't serve us. I liked it when we at least thought we were a country which strived to have God on our side. We don't belong in the ME. We shouldn't be vilifying leaders who do what's best with their nation, as long as they stay within their borders. I'll add Israel to that list of questionable friends. They benefit from instability in the ME; we do not.
MbS arrested many big $ guys in 2017, at least one of which, Alwaleed or whatever his name is, that was funding a lot of jihad crap. Billions of assets were confiscated. MbS has done many other things to moderate Islam. I’m not going to try to remember all the details but it’s happening.