Soft forks only have one valid blockchain whereas hard forks allow for the old and new blockchains to exist side by side, which means that users must upgrade to the latest software to follow the new rules.
Some criticize hard forks for being “coercive,” for forcing users to upgrade their software through network effects.
In reality, both fork types are coercive, in different ways
Soft forks value coercion over secession, hard forks value secession over coercion
Users must opt into the changes in a hard fork, whereas users have no choice in a soft fork.
Hard forks allow for a little more user freedom – they do not necessarily have to follow new protocol rules that they disagree with.
Controversial subsets of hard and soft forks
Bilateral hard forks
Ideally, two coins trade on the market, and traders decide the relative value of the two.
However, in practice, miners assign value only to maximize profit, putting their ideologies aside.
Often leads to the failure of the minority chain.
Strictly expanding hard forks
Has a strong inherent bias against the forked chain’s success.
A better option is to make the hard fork bilateral.
User-activated soft fork
Users can turn on soft fork rules without consensus from miners.
Has a strong bias for the forked chain’s success.
Miners may retaliate by creating another soft fork that causes the original one to fail.