Sure you can insulate, but that is not a model for the earth. As it has no internal combustion like a human body. The greenhouse theory is based on radiative energy transfers, not on convection. This is a key point, you really need to understand this.
You seem to be claiming that the heat energy reflected back by greenhouse gases can't be greater than the original heat energy provide by the Sun. Well, that's a nice little strawman, because nobody is claiming otherwise. Congratulations. You made a claim that I don't disagree with.
Greenhouse gasses cannot reflect anything back. There is no thermal difference for a flow to start.
The problem is you're trying to simplify this to a 4th grade understanding of science, when it's a bit more complicated than that.
They make it more complicated, if we invalidate the null hypotheses, we can disprove AGW.