I generally stay well clear of this topic, recognising that it is divisive and emotional, and not always rational - but as Australia has popped up a couple of times, I am chiming in...
Yes we had a gun amnesty and buy back after an idiot went crazy in Tasmania - perhaps ironically at a tourist site of an earlier colonial penal colony. The Prime Minister of the day pushed through the new laws against much opposition, but stood his ground against lobby and interest groups, with the support of the majority of ordinary Australians.
To the poster who said we need guns against people who bash down the doors of our homes - I point out that we are generally not facing bad guys with guns! Yes, it happens, but is not the norm. There are bad guys everywhere, but I am thankful that ours usually don't have guns... and do not want to adopt the American model. I won't argue against your model, but please do not export it.
Re mental health as a cause - hmmm. Easy to say in hindsight, not easy to predict. Perhaps better to look at why our societies in the western world are fractured, divisive and stressful. It's a bit hard to predict which individual will crack.
A look at history may help - Australia began as a penal colony but within a few short years was settled by free pioneers. That said, the British authorities had the guns, and didn't hesitate to use them against Australians promoting different views - Google Eureka Stockade for one example. (Edit - farmers and settlers had rifles too, they weren't and aren't totally banned) Conversely, if I remember American history correctly from my uni days, your vaunted second (?) amendment, the right to bear arms, came about after mad King George was chucked off and was then deemed essential - the fledgling nation did not then have a standing military, and arms held by patriotic (to the new nation) civilians was the only way to prevent invasion by the other European powers hovering around at the time. A sensible, pragmatic solution for the issue of the day. It does seem, to those watching from "outside", to have taken on a life of its own - I wonder if the founding fathers are turning in their graves at the current mindset?