It's his problem now, the way I understand it is the value of his portfolio increased during your annual tax report and he hold it through while the value of his portfolio got down to the point of 100,000$. So even if his cryptocurrency holdings is now below than his tax liabilities he still has to pay it, I am even wondering why he haven't paid his tax liabilities as of last year. Your taxing department won't probably consider the losses you incurred after every tax report you have submitted. You still have the same liability in their eyes.
Yeah this is a good point actually. And it also brings up the issue of past taxes owed. If he didn't file last year he might have been charged a good amount of interest on top of that.
in many a place not having the tax to meet your liability is your problem. At the moment of the taxable transaction you did have the money to pay it. It's not the tax man's problem if it's subsequently been lost or bet elsewhere since or more likely the overall value has just gone down.
Hate to say it, but it's actually a good point and it makes sense. You could argue tho, that with crypto-to-crypto trade you don't earn "money", so you can't make provisions for the tax due, but still you could convert appropriate portion of your cryptos to fiat... This shit can be a minefield.
That's why they calculate it as year-end finals, isn't it? So that they don't get into minor discrepancies about gains and losses along the way. There's no way that they can charge you for every gain and ignore losses. That's just not a sustainable business.
Unless it falls under gambling?