The ground in an electrical circuit is a safety feature that provides a path to ground versus a path through a person to ground.
Most 12 volt, DC systems don't have grounds and the negative serves basically the same purpose.
In DC, as in any electric circuit, the electrons, the part that is effectively the current, travels from the negative to the positive. The potential energy, which is the voltage, is measured from the positive to the negative.
Whether the fuses and circuit breakers are in the positive side or negative side really isnt an issue so much as that they are in the circuit. It's better to put them on the positive side because all the negatives eventually come together but the positives are linked to each individual circuit.
Most of the time, in a DC circuit, the term ground is used interchangeably with the term negative and is where all circuits eventually meet.
The positive side is where the electrons return through each individual component and each is protected by a fuse or circuit breaker.
That's how the circuit protection device actually "knows" if there is a high current problem and why the protection device comes after the component as far as the electron (current) flow is concerned. If the component starts to draw too much current, the protection device reacts and opens to protect the circuit/device.
I hope that helps a bit. If not, I can go a bit deeper when I'm in front of my computer rather than my phone. Easier to type than text...haha!
Red X Angler // Many men go fishing all their lives without knowing that is not fish they are after - Thoreau