Greg Scoblete notices that many Americans are somewhat confused regarding military intervention in Syria:
Another disconnect is evident: the public favors “enforcing a no-fly zone” but not “bombing Syrian air defenses.” You usually can’t do one without the other.
“No-fly zone” has unfortunately become a common phrase that often means more or less than it should. When NATO was waging a major air campaign against Gaddafi’s forces on the ground, that was referred to euphemistically as “enforcing a no-fly zone.” It is a phrase that often means whatever a person wants it to mean. In this case, 58% support for “enforcing a no-fly zone” seems to indicate that there is some acceptance of U.S. military action in Syria provided that the supporters think it is almost completely risk-free. In other words, support for a “no-fly zone” depends heavily on not knowing what is involved in creating it.
Enforcing such a thing is far from risk-free, and as Scoblete says it wouldn’t be possible to do this in Syria without destroying Syrian air defenses. I’m guessing that a “no-fly zone” means something very different to many people. I suspect the no-fly zones in Iraq after the Gulf War have encouraged the view that these are things that can be enforced without much risk and without casualties, which overlooks the extensive air campaign during the Gulf War that preceded their creation. Most Americans aren’t interested in having the U.S. wage war on Syria’s government, but many of them don’t seem to understand that enforcing a no-fly zone over another country is an act of war.
The other poll results confirm what previous surveys of public opinion have found: most Americans want the U.S. to have nothing to do with Syria’s conflict. 27% support arming the opposition, 22% favor bombing Syrian air defenses, and 14% support an invasion. As the summary states, “a majority across political party identification opposes” these other options.
Daniel Larison 
krakow 
neil 
The no-fly zones in Iraq didn’t just need the first Gulf War to establish them, they required active military operations to maintain them.
Saddam’s forces regularly tried to reestablish some semblance of an air defense system (radars, etc.). The U.S. attacked these facilities with some frequency. To forestall U.S. raids, these installations were located in densely populated areas with a vast potential for collateral civilian casualties.
The U.S. retaliated with 2,000 lb bombs. However, we first replaced the high explosives with concrete and then used JDAM, lasers, etc. to guide the PGMs to their targets.
By the 1990s, the U.S. could destroy air defense installations with rocks and we did.
Note that this was only necessary in the southern no-fly zone where Saddam’s forces operated. In the north, the Kurds held the ground and air defense suppression was not needed.