That's not how either Bitcoin or electricity pricing works. Bitcoin is secure only under the assumption that a 51% attack is computationally difficult, i.e., t

That's not how either Bitcoin or electricity pricing works. Bitcoin is secure only under the assumption that a 51% attack is computationally difficult, i.e., that it is not cheaper to acquire more mining capacity than the non-malicious miners collectively have (whether by creating a conspiracy of existing miners, or by becoming new miners) than to actually pay whatever transaction you're trying to get away with not paying. This means two things (which are, in a sense, the same thing in two different directions). First, Bitcoin needs to have a nontrivial fraction of the world's computational power in order to be secure. If mining happens on a laptop, well, I personally own at least two laptops, so I can easily double-spend coins, making the currency worthless. It doesn't have to be 51% of the world's total computational power, but it has to be enough that nobody can easily and cheaply put together enough additional power to mine false chains at a rate that keeps up with the non-malicious miners. Second, if it were ever the case that secure mining was happening on a single laptop, that would mean that this one laptop represents a huge portion of humanity's computing power, meaning that, first of all, the fair market value of being able to use this laptop would be incredibly high (both because it needs to be high enough that a double-spend attack isn't profitable, and because of simple supply and demand), and second, there would be a separate moral question of why we're using this laptop to mine Bitcoin instead of, say, powering any of the scientific research (like vaccine development) that now has to happen on TI-83s. It is technically true that Bitcoin could "work" with mining only happening on a laptop (and probably did "work" in this sense when Satoshi was developing it on his personal laptop), but that's like saying that, say, MD5 is a "secure" hash provided the attacker only has pen and paper. True, but that's not what anyone means by "secure."