If he can invade Ukraine just for shits and giggles, he definitely can order a plane to be gunned down just for his shits and giggles.
im going to do something i dont usually do and dignify you with a response:
he didnt invade ukraine "for shits and giggles", he did it because putin's got a long-standing reputation for doing things that are diplomatically unsound for the sake of maintaining his domestic cult of personality. not to degenerate into godwin territory here, but he did it for the same reasons authoritarian rulers with a nationalistic streak did it before him - you sacrifice your global image but make yourself look a whole lot better at home. Hitler seizing the Rhineland is a perfectly apt comparison - it's a territory long-considered to be Russian by the Russians, and if the rest of the world doesn't like it, they can suck a big fat one.
tl;dr putin's sacrificing his international reputation for the sake of domestic unity. and thus far it's worked for him. putin's not a mad man, he's just a politician the likes of which we haven't seen in a powerful nation for quite some time. ascribing to madness what can instead be ascribed to cold, hard politics is a mistake that we as a society cannot afford to make.
he probably didn't directly order the gunning down of the plane, thinking he has that much direct control in the micromanaging of what goes on is kind of retarded. it's like saying obama orders any random drone strike in the middle east. he has people doing that for him.
besides, from what i understand, this happened in the territory of pro-russian rebels, rather than the russian military itself. it's not too far-fetched to assume the untrained rebels got a little trigger happy.
regardless, this is a tragedy, and my condolences go out to those affected by this disastrous turn of events.
EDIT: I still don't see this escalating to the point of full-scale war between the u.s. and russia. that kind of thing just doesn't happen anymore, because we're all aware of how a war like that would end: with a helluva lot of dead people and russia's economy in the ground. It's more likely that we'll see harsher and harsher trade sanctions between the two nations before putin dies we go back to a period of incredibly tense neutrality.