"Eric, please explain how salvage has advanced the historical body of knowledge about Titanic?"
Because items from the ship are being preserved for future generations and that means that automatically the primary souce record of what was on the Titanic and what remains of her today is enhanced beyond the scraps recovered from the sea in 1912 and which have been preserved ever since. I see no reason why objects from the same ship should not be similarly preserved just because it took another three-quarters of a century to reach them. If you want to be consistent, the Halifax Museum should throw away all the woodwork recovered by the Minia.
"Can I point out that for decades people were inspired by her story without ever even seeing a murky underwater image?"
Actually, I was a Titanic buff for 20 years before I ever saw an artifact, and until I saw them I never had an emotional connection with the ship and the people who sailed aboard her. For me, it was just a fun exercise in historical knowledge to learn about the ship but that changed the day I was able to finally see them with my own eyes and it was like for the first time I ever had a bonding with the ship. So I'm speaking from my own personal experience on that score and I know I'm not alone in that experience. People bond more with history when their senses experience the objects and sites up-close, just like JFK buffs have an extra connection when they visit the Texas Book Depository, or Lincoln buffs feel an extra connection when they visit Ford's Theater and the House where Lincoln died. The Titanic belongs to that same tradition and to say it doesn't belong in that same category is to demean her importance in history ultimately.
"My opinion is that there is no justification for disturbing Titanic's gravesite."
Then why are you not objecting to the recovery from the Monitor, which involves disturbing of actual human remains, and did you object when recovery of artifacts took place from the Andrea Doria, the Lusitania, and yes, Robert Ballard's Isis? As far as I'm concerned you either must make a blanket denunciation of salvage from all ships in order to be consistent or else you're cheapening the lives of those from other salvaged shipwrecks by my reckoning.
"We know just about all there is to know about Edwardian lifestyle."
According to who? Knowledge of the recent past is not finite, and those who think it is are just resorting to the discredited "chronological snobbery" argument that says that age determines its value to history. Titanic and her artifacts have stories to tell for many generations to come, and we owe it to history to have the most complete account we can make from the ultimate primary source, the ship itself.
"We know what happened to Titanic, we know who her passengers and crew were (most of them anyway) and we know when and why she sank."
What you are doing in this statement is declaring that all further research into Titanic must now be closed because you say so, and because you feel there is enough according to your standards which says there is a finite amount of knowledge to be learned, and that is simply not how the process of historical scholarship and study works. But even those artifacts that don't tell as much as others still merit preservation, because they serve the same purpose that all the major artifacts of the Smithsonian and other museums serve and that is their association with a seminal moment in history, not their being a reflection of the broader age of history in general.
"You and others keep trying to justify salvage, but I have heard no reason other than to satisfy curiosity."
So what? If we weren't curious about our past, then the study of history would be a very poor thing indeed. Why do people go to the Smithsonian? Why do people go to Ford's Theater? Why do people go to Dachau and Belsen? It's because they are curious about the past and want to see things that help them understand it better by seeing things associated with those events in order to keep them from being dry pages in a textbook. And I find it the height of elitism to suggest that seeing the Titanic with one's own eyes should be a privilege reserved for only the elite few to dive on her in submersibles.
"Why is it that you feel such a need to interest all these people."
Because as an historian, I feel strongly about the need to preserve objects from the recent past, especially the 20th century, for generations to make use of. As a teacher I know all about how today's generation of students can not get hooked into the past by simple books alone and need the tangible reminders to make a deeper impression on them, and it'll be a cold day in you know where before I ever advocate the destruction of historical artifacts on the grounds of a dubious sanctimony that had never been hitherto attached to any other famous shipwreck.
"To me, that "preserve artifacts for the future" just sounds like a front end to "what I really want is to satisfy my curiosity, but I'll make it sound nicer by saying it'll benefit the future.""
I will turn your argument around by saying that your objection seems rooted in the desire to impose your particular standards of propriety in historical research on everyone else and to deny people of the opportunity to learn from them simply because of your own narrow objections. If you have qualms with a museum exhibition that shows these artifacts, then you are free to not visit such exhibits, but I see no reason why anti-salvors must impose their narrow definition of what is and isn't valuable for purposes of historical learning on the rest of us who do gain historical insight and deep emotional connection from these artifacts.