Russia was in Crimea and anti-Russian rhetoric / sanctions were going into effect in that time frame. So I would say people were justifiably concerned in 2015 and FB should have known better.
The Russian interference seen so far has been clumsy and of the parts that may have had an impact, they are nothing compared to Bill Clinton's open support of Boris Yeltsin in the 90s and US interference in elections around the world since forever including military coups and the assassination of democratically elected leaders.
While obviously not ideal, the rest of the world is laughing at us.
Of note, the only piece of confirmed meddling has been the alleged disclosure of voting system tampering by a whistle blower, Reality Winner, now facing hard prison time. She has received no cover from the Democratic Party. They are hawks and hypocrites.
Militaries will occasionally shoot at airplanes. Flying airplanes near active military deployments is dangerous.
Commercial airliners look nothing like strategic bombers. If militaries made more of an effort to identify targets before pulling the trigger, these types of situations could be avoided. That would actually take careful consideration and a valuation of non-combatants' lives, but hey it's more fun and easier to just blow stuff up amirite
The missile wasn't fired by the Russian military. Instead, Moscow gave some freedom fighters/rebels/terrorists an incredibly-powerful weapon and then failed to supervise them.
They don't, though. This is not a problem unique to the Russian military.