“who shoots down a warplane that “violates” your airspace for a few seconds? Why?”
Russian intrusion has happened earlier and repeatedly and appears to be on purpose.
“Syria has long disputed Turkey’s sovereignty over Hatay province, which borders Syria’s Latakia governorate, although the international community is in agreement that the region belongs to Turkey. In 2012 a Syrian fighter jet shot down a Turkish F-4 Phantom killing the pilot in the process over the region as well.”
http://dailysignal.com/2015/11/24/why-turkey-shot-down-a-russian-fighter-jet/
What is the national interest of the US taxpayer in going to war over some border incursions in Muslim Turkey. Unless you a McCain type who loves any excuse for a war, and doesn’t mind borrowing from China to pay for it, the answer is None