Anyone arguing for smart photons has some basic misconceptions in physics.
They're smart enough to follow their laws
Exactly. That's why SSDDs claims are so ludicrous.
And the claims that there is no measured evidence for such things as 'back radiation' is foolish as well. Back radiation is simply radiation. Every substance above absolute zero gives off radiation, in all directions, because of kinetic molecular collisions.
Temperature is a function of energy input minus energy output. The surface receives 165W of solar energy. The temperature is 15C which means it gives off 400W. Where does the extra energy come from? The back radiation from the atmosphere.
Why is the atmosphere warm enough to return part of its energy to the surface? Solar input, both directly and indirectly from the surface. An atmosphere without GHGs would still be warmer than space and return some energy to the surface. With GHGs it is warmer still, and returns more, because some surface energy from radiation does not directly escape at the speed of light.
We can, and have, measured the radiation coming back from the atmosphere. It is significant and without it there would be no life here because it would be too cold.
The Greenhouse Effect is both real and necessary.
Fortunately the main GHG, water vapour, works as both a heater (absorbing radiation) and cooler (evaporation, convection, clouds and latent heat). The balance between these two functions is what has kept the Earth in the 'Goldilock's Zone' for billions of years.