Wow, this was really reaching.

In the future, says Joe, people will declare: "The atmosphere keeps the planet from getting too hot in the daytime, and too cold at night time".

Straw man argument. Of course we need an atmosphere to moderate temperatures. The actual argument climate scientists are making is that we are changing the atmosphere, which changes the temperature and climate to something we didn't build society to accommodate.

“It’s quite simple. The flux of power on the top of the atmosphere is 1368 W/m^2; however, they [IPCC] say it is 341 W/m^2.”

That is a complete fabrication. There isn't one model, there are several made by several groups so it is a bit of a stretch to claim that each group is making the same mistake when the correct figure is so easy to find.

What Casey shows is that in reality, a 10,000ppm increase in carbon dioxide could, at most, reduce the conductivity of air by a measly one percent and given the actual difference between the thermal conductivities of carbon dioxide (0.0168) and zero grade air (0.0260), a 10,000ppm increase in carbon dioxide would lower the thermal conductivity of zero grade air by 0.36 percent.

Another straw man argument. It isn't thermal conduction that is the problem. It is that CO2 blocks IR radiation. Visible light passes through CO2, warms the surface and radiates IR light which gets absorbed by the CO2. The more CO2 there is, the more absorption that happens.

“Yesterday a professor tried to tell me that a blackbody (BB) would heat itself up if its radiation would shine back on it - if it was surrounded completely by a perfect mirror.

Another straw man argument. No competent scientist is saying this. But, if a body (of any colour) was heated to a certain temperature and put in a vacuum surrounded by a perfect reflector, it will maintain its temperature. We call them thermos flasks. Real ones, of course, do lose heat due to conduction and because the flask isn't a perfect reflector.