Sure, but you're ignoring flaws in the security to make a stronger marketing message for your site. Yes, there is nothing you can do about this, it's not under your purview. But nevertheless you can't make so strong a claim as to say that a message can't be faked without a broken verification function. It simply can't be faked in one particular way.

If Person B published a message under Person A's name, that is, to the non-crypto world, a faked post. They're not going to be impressed by your argument that actually it isn't faked, it's real, Person B just had access to Person A's computer.