The glass in a greenhouse absorbs a significant amount of solar IR. CO2 in the atmosphere does not, it only absorbs an insignificant amount of solar IR, which on Earth is primarily absorbed by water in its liquid and gaseous forms.
Your second quote was not from me, however, there are probably numerous factors we have yet to even discover concerning the interactions between the vacuum of space and the Earth's atmosphere, but hey, we have never let ignorance stop us before.
You are right, I quoted from another post without attribution. Your second point is also correct, ignorance has never stopped science before.
The physics of greenhouses is that the air is heated and the rising warm air is trapped by the glass barrier. This prevents convective cooling that occurs in the atmosphere.
It seems to me that clouds at night act more like a blanket than a greenhouse.