I actually really disagree about the whole diamond thing..

In addition to it being the primary plot device to get rose to actually tell her story, it plays a pivotal role in the story aboard the ship & is a key element in one of the main themes of the movie (money doesnt buy happiness).

Regarding the 1st part (wearing it for the drawing).. the drawing was intended to be malicious.. effectively a way to tell cal “we’re over”.. hence the note that accompanied it saying “darling, now you can keep both locked in your safe”. It was effectively a vulgar display to cal showing that she cant be “bought” (essentially what her arranged marriage was.. selling her as effectively a slave so that her mother would remain wealthy).

Regarding the shooting scene, id argue it wasnt about the diamond at all, but about what happened just moments before… jack and cal were both trying to get rose on the lifeboat. It was super macho aggressive where they were both kind-of attempting to one-up eachother to win her affection (hence cal removing jack’s blanket and giving her the coat). This is also when cal gave his “i always win, one way or another” remark. Rose jumps back onto the ship and right into jacks arms (passionately kissing in front of cal). Enraged by this, cal chases them with the gun.. id argue, this is cal’s last ditch attempt of “winning” (attempting to force them apart through murder). I think the comment about the diamond was just more of an afterthought once the adrenaline wore off.

Regarding throwing it overboard, what was she supposed to do? Give it generously to bill paxton? Rose’s entire presence on the modern ship & all of her actions are purely malicious. Bill paxton getting the diamond is literally the worst case scenario.

Think of how rose got involved.. Bill paxton was showing off the drawing on tv to essentially say “see, we arent grave robbing, we are simply preserving history”. Rose saw right through that though due to her knowledge of where the drawing was (in the safe). Her phone call to bill paxton saying “have you found the heart of the ocean?” Wasnt a sincere question, but more of a “i know exactly what youre doing” threat. She is there to stop them, not reward them.. her excessive luggage & wasting a whole day of their time to ramble about old grandma stories prove that. (on a ship like that, schedule is everything and wasting a day to listen to old grandma stories is most certainly a worst case scenario that will cost them millions).

Sure in theory, she could sell it, but doing so would create 3 issues..

1- the sale of such a priceless artifact would garner tons of attention. Everyone with even the slightest potential stake in it would likely come after her with an armies of lawyers (think insurance companies, cal’s heirs, the UK government/royal family, bill paxton’s company, etc).. Sure, enough time has passed that different statutes would limit their effectiveness in achieving success, but she (and her family) would be put in a precarious position of spending years entangled in legal battles while simultaneously being both “rich” and “not rich” (cant exactly buy a lawyer with a diamond that may or may not be yours after the fierce legal battles)… its really being stuck between a rock and a hard place.

2- it would go deeply against her moral compass. Her entire life story was essentially being enslaved by wealth & escaping/ living an amazing life it by essentially faking her death to become poor.

3- The diamond is really the only tangible item associated with her past life, jack’s entire existence, and an event that played such a pivotal role in completely changing every aspect of her life. likely not a single day goes by where titanic isnt in her mind… Considering this, id argue the sentimental value of such an item likely holds more value to her than all the money in the world.

Personally, I always saw her throwing such an item in the ocean being similar to putting a cherished possession in the casket of a deceased loved one.. frankly, i think it is the single most profound scene in the movie. Ive watched the movie literally hundreds of times & that scene is without fail when i start crying. The solitude nature of the act coupled with the look of relief on rose’s face just get to me. Its like shes been holding her breath for the last 84 years & that moment was the first time she was able to finally breathe.