"How come Syria’s air defenses present a problem for US aviators but not Israeli pilots?"

"... To date, the answers to my questions about Israel’s capability to penetrate Syrian airspace and American disinclination to do the same and more generally concerning intervention in Syria amount to the following:

1)  Israel’s brief incursions are different from the sustained campaign the United States—and presumably allies—would have to undertake to establish a no-fly zone (NFZ) in Syria.
2) Israel’s missions have been on the “periphery” of Syria and have never had to contend with the dense network of air defenses  in and around major population centers.
3) The Assad regime has placed air defenses within population centers, putting both Syrian civilians and American aviators at risk during any air campaign.
4) Intervention in Syria would be costly and detract from the U.S. military’s ability to conduct operations in other areas.
5) Syria is complicated and military intervention may not help the situation; in fact, it might make the situation for Syrians a good deal worse.

With the exception of the last, none of these claims is convincing either in part or whole.  It is true that enforcing a no-fly zone is an entirely different undertaking than Israel’s bombing of a Syria-based Islamic Jihad training camp in 2003, the destruction of Syria’s suspected nuclear facility in 2007, or high-speed overflights of Latakia intended—literally—to rattle Bashar al Assad in his summer palace in 2003 and 2006, but that does not mean the United States should not or cannot prevent Assad’s forces from flying...."