Collision resistance is critical for most applications of the OP's scheme. The OP is proposing using hashes as identifiers for immutable content. Imagine the following:

- I publish a JavaScript library under this scheme using a hash without collision resistance.

- Popular/important websites refer to my library as hashname://..., trusting that this refers to the version of the library that they audited.

- I can then create a new, malicious version of the library that has the same hash and use it to infect popular sites.

Allowing collisions breaks the immutability requirement, which impacts security in many important cases.