I'm not actually aware of any particular example where the government taking away guns has then been followed by some sort of citizen catastrophe, let alone enough cases to describe this as 'often'.
Hitler, of course, did in no way disarm his citizens, only the Jews- and this, of course, was part of a much wider programme of Jewish persecution, not some cunning, advanced preamble. In broad terms, Hitler actually relaxed most gun control laws compared to the Weimar Republic. And in any case, having guns would not have protected the Jews one bit, seeing as it was mostly other (and logically speaking, also armed) citizens that were turning them in, and in any case the Jewish resistance movements found guns easily enough (it being war and all).
Asking whether there should be an argument at all is also a bit weird. The Second Amendment is a literally extraordinary piece of legislation- it is very unusual in global terms and its existence does need proper justifying. Justifying it on the grounds that 'otherwise the government might come and oppress us all' is also in of itself an extraordinary claim that needs justifying. I'm sitting here in the virtually guns-free UK and feeling pretty liberated, all things considered. Also with very low gun crime.
Not that these things are instantly transferable- there's a cultural thing with guns in the US that would take more than a law change to sort out. It'll be a generational thing to ease the guns mentality out of North America. In any case, the text of the Second Amendment is a joke in modern day terms- a 'well-regulated militia' has pretty much no connection at all to what we see the SA used for in the modern day as the whole idea of citizen militias has gone out the window, in the US as much as anywhere. The circumstances under which this law was created no longer exist, so this is now more an argument about defining what the US actually is, culturally.
As per the topic- plenty of people saw this as an Obama thing but there's little evidence for that other than that a lot of gun control advocates wanted it to be him because it makes an easy focal point for them to rally against. After all, it's been stopped from happening, and if this really was Obama throwing his weight around, he would have done it anyway as he doesn't give a damn about the arguments raised against it.
As for banning assault rifles vs. handguns- no doubt, handguns are the far more dangerous thing. But they'll be the last to go as they are the most widely carried thing; you can't start there in the US because of the mentality (in most countries with gun control laws, handguns got taken out first). The assault rifle look of the AR-15 is symbolic- it represents the militarisation of segments of American citizen life. As I am of the opinion that said militarisation is a problem, banning such guns would be an excellent first step.
It'll be a LONG time before this is done- I hope in my lifetime but we'll see. In the long-term, though, the US cannot isolate itself forever and its exposure to global influence will erode these erratic parts of its culture- just as it is finally giving way on healthcare, even if only in small ways.