In the longer-run, deterrence should result in lower costs than would otherwise be the case. Where deterrence fails, conflicts can erupt and conflicts are far costlier than deterrence. Putting aside political arguments concerning the recent war in Iraq, there's little question that on a present value basis, the costs of the war were vastly higher than those associated with maintaining the prior containment regime. Moreover, the human costs were also vastly higher. Furthermore, following the war, one found that the containment regime had worked remarkably well as Iraq had been deterred from relaunching its WMD activities.
Democratic movements have largely internal origins. The fallacy that has influenced American foreign policy since at least the time of President Woodrow Wilson is the idea that all peoples everywhere want democracy. The quest for individual freedom has been a strong one throughout history, but that quest is not exactly the same thing as desiring democracy. Moreover, the aspirations of people are, in part, a function of a society's structure (institutions, economics, culture, etc.) and history. The fundamental Sunni-Shia divide is part of the reason one has witnessed illiberal regimes in the Middle East. The peoples see things as a zero-sum game where one faction can only gain at the expense of the other (no "win-win" conceptions) and that strong rule is required to prevent societal fragmentation along sectarian lines. Western idealism assumes that authoritarian rule is largely an accident and that "regime change" can, therefore, quickly allow for democratic forces to take hold. The evidence has not been kind to that assumption.America has troops in over 150 countries, props up corrupt regimes, bombs other countries at will (which is a technical act-of-war), gives away tens of billions in arms to whomever it wishes and has caused tremendous death and misery (directly and indirectly) to many countries that it decided to ram democracy down their throats/change governments they don't like.
Not only is it wrong, hypocritical (Obama freaks out about a referendum in Crimea but embraces an illegal coup in Ukraine) and causing much hatred against Americans (for drone strikes, supporting horrible regimes like the Saudi Royal family, Gitmo, etc.)...it is (partly) bankrupting the United States.
There's also a tendency for the U.S. to view others as we view ourselves. Hence, the sectarian uprising that followed what had been protests for democracy was quickly lumped in as a democratic revolution in the tradition of the American revolution, democratic yearning in Eastern Europe during the Soviet era, etc. The reality is that a repressed majority was simply seeking to gain control over a brutal minority-led regime. Consistent with ethnic conflicts, brutality was in abundance and liberal ideals concerning humanitarian protections were discarded to the greatest extent possible.
Regional uprisings were quickly coined the "Arab Spring" in an analogy to the democratic Prague Spring. Not surprisingly, given the region's structural and historical context, the democratic illusions have proved largely unfounded.
The focus on national interests and strategic allies would preclude the use of force in such situations. Diplomacy and other non-military programs could "test" possible democratic aspirations, give support to genuine movements, and limit the risks should those movements prove less than democratic.
In terms of Saudi Arabia, among other non-democratic states, the U.S. has to deal with the world as it is. The U.S. can't dissociate from dealing with such governments when U.S. interests are at stake. To do so would simply be the other side of the coin of military interventions in the name of ideals. In this case, the U.S. would refuse to engage in relationships in the name of ideals. Both approaches are extreme polar opposites. Constructive relationships are often necessary in advancing the nation's interests and promoting stability. Of course, the U.S. can and should use its soft power to encourage improved human rights, etc., and influence the factors that might lead to a more favorable climate for democracy. The latter would require a lot of time and patience, as societal structures evolve slowly.