If you're thinking of the physical goods being transported:
* Passengers: This is the most direct opposite, as it refers to people being transported instead of things.
* Mail: This contrasts cargo in terms of size and type of goods.
* Baggage: This focuses on personal belongings instead of commercial goods.
If you're thinking of the act of carrying or transporting:
* Discharge: This is the opposite of loading cargo.
* Unload: Similar to "discharge," this refers to the removal of cargo.
* Deliver: This implies the final destination of the cargo, while "cargo" focuses on the transportation process.
If you're thinking of the space used for cargo:
* Passenger space: This contrasts cargo space with space for people.
* Hold: This is a synonym for cargo space, but can also be used to refer to a specific area for something else.
The best antonym will depend on the specific context of your sentence.