Due to the right handed coordinate system chosen, each of the six particles is simply the same particle rotated one way or another. This is a particle with a charge of one. Thus it is natural to call this particle a proton. By looking at the geometric structure of the quarks that make up a neutron, one can easily see that there are two negative attachment points and two positive attachment points. This allows neutrons to bind to themselves or to protons.
Protons only have two positive attachment points.
Thus protons cannot bind to themselves. Geometry can be used to show why the neutrons do not increase uniformly in the periodic table as well as why there are isotopes of various stabilities. Neutron stars can form but not proton stars because only neutrons can bind to themselves.