There's currently a post on HackerNews called The “432 Hz vs. 440 Hz” conspiracy theory. It links to an article by Jakub Marian that starts to break down why he doesn't feel it's a conspiracy theory.
While I appreciate Jakub's breakdown for the reader to get to explaining why the 432 number itself is effectively fabricated for convenience, he eventually states: "The 432 Hz tuning, the divine tuning of nature itself, is ultimately defined as one vibration per 21279240.2083 periods of radiation of an uncommon chemical element" however he's missing the critical argument.
What is missing from the argument is the irrelevance of the number. For example, if 432 Hz resonates with I don't know, the neocortex, there is no relevance what the number is or that we've associated with what we humans currently call a time second -- that's just a standard way of identifying the number.
What needs to be done is validation or invalidation of this frequency in terms of "healing and soothing properties." It's also important to not do so defensively, otherwise you're arguing against organized religion or Santa Claus or Unicorns -- it's a useless effort to argue against something that has no scientific evidence. If someone is making a claim without evidence in the first place, you're arguing irrationally already and you've already lost. Reason requires logic.
"Here is my repeatable scientific evidence why I feel the world is flat" is different than "I have a feeling the reason the sky is blue is from unicorn tears -- prove to me it's not".
It is my suggestion that if someone feels that 432 Hz has healing and soothing properties, they take this hypothesis and run it through the scientific method. It will be these published results that can be responded to, directly. A quick search on plosone doesn't show that there's any documented research in this area currently, a new opportunity for those interested.