As much as the idea of "holographic rights" might seem ridiculous from a real-world point of view, it's definitely not a non-issue within the Trek universe because holograms are capable of reaching sentience. And as Optimus Prime would say, "Freedom is the right of all sentient beings."
If artificial intelligences could not attain sentience, Bry, what does that say about Data? How is he any different from Voyager's EMH? The only real difference is what their bodies are made of. If humans (or Vulcans, or whatever) can create a sentient positronic life-form, why can't they create a sentient holographic lifeform?
In my mind Data's status is partly because of his unique nature.
In "The Measure of a Man", it is Data (not artificial lifeforms as a whole) that is given equal status, so what he achieves isn't immediately applicable to Lore (Juliana Tainer would be a grey area however, seeing as she doesn't know she's an android). B4 would need a ruling of his own (just because he looked to become Data 2.0 doesn't mean he is Data, his more simplistic manner might mean he is incapable of making the same choices and decisions). B'Elanna states in "Prototype" that Starfleet has lots of robots but only one (Data) has equal status.
It is obviously extremely difficult to build such a complex and advanced android (Data only tries it once, and all of Doctor Soong's earlier versions were a bust) that is capable of achieving sentience--otherwise we'd see at least one on every ship and station in Starfleet. It is this uniqueness that gives Data his own place within the Federation, where he has the same rights as a flesh and blood person.
Holograms are a dime a dozen. Yes there are those who have are sentient so as to perform various tasks and roles (the EMH programmes, Vic Fontaine, Professor Moriarty), but the vast majority are programmed to be characters. Would a ruling on holographic rights apply to all of them (would T'lana from Vulcan Love Slave refuse to participate due to the exploitative nature of the programme) or just those deemed sentient, and what would be the definition of that requirement? And when holograms can be so easily made and manipulated, would that not mean that any and all of them could be upgraded and deemed sentient--which would destroy countless programmes if a character decided not to play their role or wanted another part.
What then does that mean for a starship's computer core? Depending on the definition of sentience for holograms, couldn't it be applied to advanced computers? It would never end.
Had it just been the Doctor looking to be recognised as a unique individual, for all he had developed, learnt and experienced, I would be more willing to accept the concept. Though for all holograms just seems ridiculous to me.
But then, that is just how I see things.