the seed is public, you can make a private world, go into spectator, and do all this. This is just a convenience thing for the server version. IMO it just keeps people using the server version and bringing the community together.
I see no problem with it.
also, if i'm going to cheat to find diamonds, thats not how i'm gonna do it. I'm just gonna get an x-ray mod.
You can only see diamonds that are exposed either air or lava. thats a minority of the diamonds. I honestly think it would be easier to mine the diamonds the normal way, rather than find them in spectator, write the coordinates down, go to survival, dig to that spot, and get the diamonds...