  Blockchains are still perceived chiefly as a new technology. But each
blockchain is also a community and a social experiment, built around social
consensus. Here I discuss three examples showing how collective intelligence
can help, threat or capitalize on blockchain-based ecosystems. They concern the
immutability of smart contracts, code transparency and new forms of property.
The examples show that more research, new norms and, eventually, laws are
needed to manage the interaction between collective behaviour and the
blockchain technology. Insights from researchers in collective intelligence can
help society rise up to the challenge.
