Truly democratic governments in Arab and other Muslim countries might well turn out to be anti-American and anti-Western because of vast cultural differences (especially related to treatment of women) between countries dominated by secularists and countries dominated by observant Muslims, but that doesn't necessarily mean America should support entrenched dictators either. I think America (and other democratic nations) should endorse and support their own values whether or not they obtain any immediate direct benefit from doing so.
During Jimmy Carter's Administration, America started demanding that its Latin American allies go democratic, which demand didn't exactly endear Carter to dictators that dominated those nations in those days. They held out, hoping that America's next Republican President would be more understanding of dictatorial prerogatives. That next Republican was Ronald Reagan, who surprised Latin dictators by making similar democratisation demands. Latin America rolled over quickly thereafter. Less than 8 years later, demands for democratisation became so strong in Russia that America's primary post-1945 existential enemy collapsed internally. There may have been no direct connection between America's actions in Latin America and what happened in Russia, but there may well have been indirect connections.
Talk of throwing America's "full weight behind the Syrian rebels" only began when it appeared that Syria's pro-democracy movement was likely to descend into chaotic civil war. America doesn't "win" if Assad stays in office, but it also doesn't win if Sunnis backed by Saudi Arabia (and Iraq's chapter of al-Qaida) take over and begin to murder Shias and Alawites in large numbers. Given that "no-win" situation, America might just as well act in accordance with its own values and let those chips fall where they may.
Meanwhile, Saudi Arabia's monarchy has played its cards surpassing well. It has effectively bought off America's Republican Party, its ambassadors have become everyone's best friends and indispensable party throwers in Washington, and rumour has it that Saudis may have had something to do with Obama getting into Harvard Law School. No one, left or right, will argue for energy policies in America that would cause Saudi Arabians even slight indigestion. American politics have long been for sale, with your Supreme Court's recent approval, and Saudi princes know how to bid for influence as well as any Super-PAC contributor. Don't like Saudi society? Too bad. All you could really do about it would be to vigourously promote fracking, something many Americans won't tolerate even if their dependence on Middle Eastern oil sucks them into even more wars to secure supplies.
Most evil? Saudi Arabia may be more culturally alien from America and other Western countries than any other (even NK ostensibly believes in women's rights on some levels) but America has supported some amazingly bloody and repressive dictatorships in its day. We have yet to see pictures of untold numbers of dead Saudis piled up in open pits, if you catch my drift.