Sentient holograms like Vic or Moriarty were only sentient because they were specifically made to be sentient.
Problem there is there is no evidence that Vic was specifically made to be sentient. He was created as just a average holodeck character.
Do they have the right to know if they're being simulated in somebody else's *mind*, for the same purposes?
But that isn't using technology to deliberately create a interactive physical and psychological reproduction of the person.
Leah Brams was a intellectual and psychological reproduction.
If the holodeck computer is in fact temporarily creating sapient beings
Which it isn't.
Why do holograms talk to each other when there are no "real" people around to hear them?
Is sapience the norm for holodeck creations. Consider the police detective in The Big Goodbye, McNary asked Picard
"When you've gone, will this world still exist, will my wife and kids still be waiting for me at home?"
Now if it's just Picard talking to the computer, why would the computer say that to Picard?
In a earlier scene, Picard leaves the holodeck, the doors close behind him and the "arch" disappears. Then after Picard is gone the character of Lech enters the room Picard left and calls to him (this was before the Jaradan probe). Why would the computer say that to a empty room?
Troi mentions in The Big Goodbye that the holodeck had received upgrades. One of the consequences of improvement to the holodeck (perhaps unrealized) could be that the holodeck was now creating sapient beings. And I'm not just talking about the holodeck on the Enterprise.
What I'm suggesting Mr. Laser Beam is that their technology has advanced to possessing this ability, maybe without them fully understanding that they can do this.
Yes you could create just a image, but once you tell the computer that you want a fully interactive hologram they become a person.