In principle, I agree the world is better off without murdering ideological tyrants like Saddam Hussein. Our problem is Rand Paul makes several good points, all with realized implications.
Knowing how terrible Saddam was to his enemies there was a reality from his rule. His methods made it where just about everyone in the nation was terrified to make too much trouble for anyone else, usually with the understanding that Sunnis and Shiites did not have the room to exploit their differences. One ruled, the other was terrified.
Now that Saddam is gone, the installed government is too weak managing a military that is far too weak to control all of their nation. Part of the reason that ISIS was successful in getting such a foothold in Iraq was because of this weakened condition we are responsible for. A strong argument could be made that ISIS would not have the ability to make such a mark in Iraq if Saddam (or someone like him) was in charge. Does not mean we would be able to escape Syria's weakness, but it still makes a statement about how power is better ensured.
What we know is ideologically most of the region subscribes to a religion (some splinter of) that has a baked into the text method of social control and order. Or, the merger of a government ideology with a religious ideology where strong "authority" becomes hallmark. And usually with a rather restrictive tone. It is a core reason that western governmental ideologies have challenges handling conditions in the Middle East, I would argue the people themselves ideologically do not have the aptitude for "freedoms" or "tolerances" as we would describe them. A theocracy of some degree ends up what runs these nations.
What we see today is a perfect example of what weakness in that region of the world yields. A hotbed for even more extreme ideologies to bully their way into power, because at the end of the day there is no one else strong enough (and/or willing enough) in the region to stop it. Been that way for a very long time.
Consider those we are allied with, in the region with similar ideologies based on a flavor of the same religion. Anyone really want to make the argument that Saudi Arabia is not a theocracy? Not a strong organizational government with that merger of "religious authority" with strong social controls? That truth, if Saudi Arabia did not have that form of government they would end up in chaos. Shuffle on over to Turkey and try to convince us those are not strong centralized ideological and authoritative nations. Perhaps to a lesser degree but still, a flavor of the same religious ideology that is anything but tolerant or a "free" society. We going to try to say Afghanistan was successful with a strong new government when pockets of the nation still lean Taliban?
Expand out that consideration for those we are not allied with (or if so, with real conditions.) Like Egypt, or Libya, or Syria, or Iran, or the Palestinians, or Yemen. Again, without a strong hand running those nations then someone else takes charge (or tries to) usually to problematic results. Anyone really think we would not come to Syria's aid if they were not aligned with Russia?
This is one of the many reasons I harp on our hypocritical and confusing foreign policy, if you look at the chain of who likes who and who hates who in the region it really is an epic disaster. But, the nations that are most calm odds are have a strong ideological government keeping it that way. Some how. There may be an exception here and there, but it is a sad reality given what we are really talking about in social dynamic in these nations.