In the end, blockchain is a database format. It’s not like relational databases changed the world. Oops, yes, they did…
So probably a consideration about negative effects of blockchain should frame it as a comparison to how thing would go down in cloud-based relational databases were to be deployed instead of a blockchain.
In that light, I see mostly two gradual shifts which in the long run can have major consequences but on our economic and our political system — both good and bad.
The first effect is that blockchains reduce the comparative complexity of transacting across markets, which means value chains which currently still happen within firms shift to markets. Sharing economy is a primary example. From a global trade and a labor market perspective, the negative consequence would be an increase in the disparity of wealth, exacerbating the trend we’re seeing now. Rents will increasingly be reaped by ever smaller economic units, unless we find a potent countermechanism.
The second effect is the tokenization of payment systems, which, if it takes off, will lead to shared currencies among “economic basins of attraction” rather than geographic ones. The negative side effect is an increased divide between urban and rural economic power. At the end of that road is the dissolution of geographic political units (vulgo: nation states).
Blockchain doesn’t “cause” either of these trends, it simply accelerates their effect on society. Also, we shouldn’t really look to a database format to solve society’s ills. The harmful side effects of economic and geographic inequality can be tackled politically if the root causes are understood. But even without blockchain we’re not anywhere near to that…

