Yemen is a complicated situation with a proxy war between Saudi Arabia and Iran neither of them are particularly bastions of human rights or values.
Unlike Iraq there isn’t a substantial enough Shi’a population in Saudi Arabia to serve as an Iranian proxy to fill the void.
The other two major Sunni powers in the region are AQAP and ISIS both of them are far worse than the Saud family could and would ever be.
Pure and absolute moral objectivism is just as bad as pure moral relativism.
While you can assert that we should never support such regimes, let them fall or even actively push for a regime change on pure moral grounds you aren’t the one that needs to deal with the fallout on the ground for years and decades to come.
Regardless of how bad the situation in Saudi Arabia is now it can always get worse, much worse and I don’t think that you should advocate for a social experiment you wont be willing to participate in.
The world's majority Muslims are Sunni, does that make AQAP and ISIS the mainstream? Absolutely not. They have been used as a red-herring before (not that I am saying it is something that can be ignored) for oppressive regimes to continue (e.g. Egypt, Syria), as they are nowhere near powerful enough as they are made up to be. That is precisely the reason they rely on individuals to attack civilians at western countries. Also, no one is calling for a regime change, that is what US and its allies do unless they don't like the person in charge. In this case, they like Bin Salman.
It’s not about liking or not liking the person in charge it’s about being able to do something about it without causing even more mess.
The entire region is royally fucked with the exception of one country and it’s not just the US (NATO) and Russia (USSR), not to mention colonialism to blame.
Heck look at the election results in Lebanon this weekend, they are perfectly capable of fucking themselves over without any US intervention.
P.S. If your measure of power is ones ability to attack the US at home then by that definition alone AQAP and ISIS are the most powerful entities in the region as no one else has any logistical capabilities to project their force outside of their geographical sphere of influence.
In a hypothetical scenario possibly the only one in the region that could do that currently is Israel if they modify their satellite launch vehicle into an ICBM and even It might not have the range to hit the continental United States with any payload.
The Iranians are probably half a decade away from a similar capability.
They might be able to use the stronghold they established trhgouh Hezbollah in South America but that wouldn’t be any different from the asymmetrical warfare AQAP and ISIS are capable of implementing just with an IRGC flare to it.
No one in the region has military bases within striking range of the US,no one has an aircraft carrier, no one has the logistical capabilities to wage even a ground war further than a few 100’s miles from their borders.
Houthis being armed militant does not excuse the blockade of essential supplies that is leading to the death of thousands of children.