> This is an oxymoron. How can you mathematically enforce a purely social concept? Property rights aren't tangible things; they are creations purely of law and of the societies they inhabit. Can you mathematically enforce that no one build a house on the land I own? That no one picks an apple from my apple tree, except with my permission?
Land or an apple tree aren't natively digital assets. So no, they cannot be cryptographically enforced. Bitcoin is natively digital. If I alone have access to a wallet (i.e. memorized a seed-phrase), my rights to that bitcoin are enforced cryptographically and defended by the power of the network. "Ownership" meaning I have exclusive rights to "spend" them.
"Social construct" still absolutely comes into play though. The social construct is money. Bitcoin being money is a manifestation of a social construct. Are you suggesting something being a social construct means that they are not "real"? Because that would be a MUCH larger debate.
> I just don't see how cryptocurrency helps the unbanked--what does it bring that M-PESA doesn't bring?
A trustless and self-sovereign way to store value? This becomes increasingly important the more corrupt your Government is. For example, if your government wanted to freeze your money because you participated in a protest they don't like.
> Furthermore, how are those benefits worth the externalities of cryptocurrency, specifically the massive energy consumption that undoubtedly fuels the climate change that is slowly worsening the lives of many of the unbanked it's purporting to help?
Electricity consumption, in and of itself, does not fuel climate change. CO2 emissions do. Also depends on the relative climate cost between one system and the system it looks to replace. For example, electric cars are bad for the environment if you look at them in a vacuum. But, they are better than ICE cars. So they are applauded.