…what is there to net out the photons? Netting out to zero requires too many special circumstances IMHO.
Photons are their own antiparticle because they have neutral charge, which, to, nets out.
Netting to zero is the whole circumstance.
There are two and only two stable matter particles in free space, the electron(-) and the proton(+). (Note that a neutron is fine in a nucleus but in free space it decays in 10 minutes or so.)
It very curious that this number is limited to two. It’s as there are only two ways to make them or only two ways that are stable. Either way, it makes sense because the 4th-dimensional axis that nullifies all of existence via opposite charge polarity has only two degrees of freedom.
So, there can be no stable neutral matter particle and there can be no other stable charged matter particles beyond the electron and the proton (we always include antimatter) since the Cosmos can be no other way than this in this regard. Presumably, a neutral matter particle could not sum to nonexistence, as it could not be part of unit polar volume (which is half of unit hypervolume).
There is only one stable neutral energy particle, the photon, and, again, this could be no other way. Nor can it have an antiparticle at all. There can be no charged energy particles. A photon represents unit hypervolume and so it cannot be a part of unit polar volume like matter particles are.
No other kinds of particles can be stable. This reflects the basis beneath.
Unit hypervolume is hc / 2pi; unit polarvolume is hc / 4pi. (The 2pi part comes from the trigonometry of the sinusoidal wave of the photon, having to do with the photon scaling factor)
It’s really particles versus their 4D antimatter mirror twins of opposite charge that nullifies all of existence in the overview, which in reality can’t happen in actuality because a lack of anything—nothing—is a perfectly unstable state. This simplest state is what is expected as the TOE, as all the ever simpler and simpler entities beneath higher reality points the way to it.
Boring answer? Nope, for an ultimate answer can never be boring.