i feel bad for the people who get their coins stolen and noone believes them and they are forced to pay taxes on stolen coins. that would really suck
That seems to me like it would be a legitimate loss and could not be subject to tax in any circumstance. I've yet to hear any guidance from any government dictating how to store BTC in order to guarantee no loss.
Not only is this a potentially handy avenue for plausible deniability, but it is also a grave and legitimate risk. Indeed, that is part of the reason it is so plausible.
I've left a trail of lost BTC along the path, and a much bigger trail of donated BTC which I've not kept records of. That is, in fact, the truth, and I suspect it is for many of us relative old-timers. Fortunately I happen to be able to account for the BTC I acquired with some precision having done so in a relatively narrow window of time and mainly through an exchange who kept convenient records for me to download.
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As I was writing this, it just occurred to me that one approach a government might take to 'attack' Bitcoin would be to say, "Ya, it's cool to have BTC, but you need to store them in
our on-line wallet service since we can guard against loss and illegal conduct." And relatedly "If you have nothing to hide, you have nothing to fear."
An advantage to this method of attack is that most people do not know much about Bitcoin but do see it as a potentially dangerous thing often used by criminals. And of course, they have no BTC themselves so it's not as objectionable to the. Such a strategy might appeal to a broad swath of individuals many of who would consider a total criminalization to be unfair and uncalled for.