Vitamin D is actually a prehormone and only attains the properties of a steroidal hormone when converted to calcitriol via the kidneys, which again is a level determined by the body.
The information and links you have posted on in relation to Vitamin D having immunosuppressive effects, only occurs when supplemented with (to quote your first link) "massive doses".
No one John is advocating "massive doses", only those doses that are beneficial and optimal for the body.
Your body needs water to survive, but in excess will kill you.