The serious problem I see here is that even after he indicated he is not able to talk to them they refused him to use pen and paper. I also have a speech impediment and carry those with me. Taking them away and not letting someone use them when they are already frazzled and upset is like asking someone in the wheelchair to just "stop being a pussy and get up and walk" or accusing them of "being uncooperative".
Furthermore, he's attempting to advocate for others who may also not want their disability known. He gives up his privacy in a certain setting in order to (hopefully) allow many others to never have to give up theirs.
Speech by choice is very different than being unlawfully questioned and to have your possessions, medical liquid or otherwise, held hostage contingent on your reply.
As far as reasonability - he's correct in noting that the TSA is not entitled to your medical history. Moreover, TSA screeners are generally not doctors (some may be), they're not YOUR doctor, and they're certainly not in a position to decide what is or isn't medically necessary for you.
Does this mean that you should be able to get your juice past security by claiming to have a medical condition? No.
It means you should be able to do that without having to disclose anything about your health, and the only remedy that should be available is for the TSA to screen the liquid if they feel it is necessary to ensure passenger safety.
Is that unfair? Maybe, but so is a ridiculous ban on a liter bottle of safe substances.
On the other hand, in your own forum while making a point, it makes perfect sense to use that context to explain why it was embarrassing and is in need of proper training or policy modification.