I agree, they're not "secret", they're not "hidden" either; and, I think, that viewing a hidden photo under most circumstances should require an explicit action.
And I'm making a stink because the UI says one thing and does not deliver:
This photo will be hidden from Moments, Collections, and Years but can be found in the Hidden album.
As it stands, it more accurately reads:
This photo will be hidden from Moments, Collections, and Years but can be found in the Hidden album (or All Photos, or Last Import, or Favorites, or Panoramas, or Videos, or Bursts, or any album you have manually added it to).
Yeah, I still think it reasonable for a hidden image to remain so in all views unless Show Hidden is selected; and I generally feel this feature is not implemented well.