I posted the aerogel paper to see if anyone would try to engage in a thought experiment. That would require someone to question what an aerogel is, what it’s used for and think about why having something with the density of air, near zero thermal conductivity and oh-by-the-way-can-be-custom-configured-to-block-different-types-of-radiation would have an incredible potential for space travel.

Which is very different than actually providing an explanation of how aerogel could actually be used to block cosmic rays.

Cosmic rays aren't electromagnetic radiation. They are instead extremely high-energy particles that travel through space at very nearly the speed of light. Completely different physics.

There's no implied "thought experiment" here - it's like posting an article about some new antibiotic and asking people to think about how it might be used to treat a virus or radiation poisoning. The fact that some technology exists to solve problem X does not mean that it has any applicability to solving problem Y - and posting an article on something irrelevant to the problem being discussed isn't "seeing if anyone would try to engage in a thought experiment," it's just profoundly misunderstanding the vast difference between X-rays (and other types of electromagnetic radiation) and cosmic rays.

Who did that?

You did, when you truncated my sentence to just "we can't" from "we can't shield against cosmic rays with any currently-existing technology." If you think there's current technology that can provide spaceships with shielding against cosmic radiation, then just explain how. Otherwise, you're just engaging in wishing away the actual impediment to space exploration.