I totally get this, but a hackathon is a one time software build and you don't need to lean heavily on a schema if you've only got one state your data has ever existed in, MongoDB is great for templating like this.

However, when it comes to writing software that's meant to survive changes and versions the schema ends up providing a safety net that ensures you can ignore the data that exists and assume that the structure described by your schema is consistent. Data integrity is key to maintainability and those constraints are what keep your data clean.