[ars]

That is not true. A perfectly reflective silver object still emits blackbody radiation.

And a perfectly blank one will absorb light, heat up and also emit blackbody radiation.

[nobody3141592]

A Mr Kirchof would disagree with you if he wasn't dead.

A perfect emitter facing an infinite cold sink is in perfect equibirium at the temperature of the cold sink.

[ars]

Of course - but that's not what you said.

You said: "...would cool to -270C however much power you dumped into it" and that is not true.

And in any case you don't need to be a perfect emitter to be in equilibrium with the temperature of the cold sink, all you need is infinite time, but any emitter, no matter how bad will eventually equilibrize.