I wouldn't kill off anyone "just because."
Agreed. A death that is structurally sound, rather than contrived, can be very effective for the story and the viewer, and still allow for a satisfying, uplifting ending.
Forrest's death in "IaMD," for example, was structurally solid. He was the captain, and he stayed on the bridge, making sure his crew had time to escape, before he went down fighting. Even in the MU, Forrest was noble at the end.

Forrest's death in "The Forge" worked for me too, since he didn't hesitate to sacrifice his own life to save another.
Someone told be that every Star Trek finale needs to have a death in it; a little misery.
Joss Whedon often kills off main characters to remind us all that shit happens, and that life is fragile and shouldn't be taken for granted. In more effective stories (Joss's or whoever's), such deaths are thematically/structurally "earned," that is, properly set up rather than arbitrary. Spock's death in
Star Trek II is a great example.
Conceptually, I have no problem with "killing off" Trip in the finale - I just wish it hadn't been handled so stupidly. I would have given him a more thought out, deliberate death, and a proper mourning.
What she said. I didn't consider Trip's death particularly satisfying (structurally) because his actions seemed inconsistent with the way he had been portrayed earlier--even one episode earlier--in which he had the smarts to get out of far tougher fixes, without choosing the lowest-level solution, i.e., get hisself blowed up. And other than the scene in Trip's quarters between T'Pol and Archer, nobody seemed affected by Trip's death, which worked against the death being an emotionally affecting, heroic sacrifice.
Were it not for the pseudo-canon bio in IAMD, I think Archer's death might have been interesting. I think he would have faced death with honor and equanimity; it also would be consistent with his unhesitatingly self-sacrificing nature that we saw so many times from Broken Bow to Terra Prime. It wouldn't even need to be all Archer-go-boom. I can imagine him just quietly doing what needed to be done in order to save his crew.
That would have been perfectly in character for Archer. Look at his "death" in "Zero Hour"--in character, high stakes, getting the other crew to safety first, and a sacrifice to save the world. And we
saw the aftermath, in the grief of his closest friends and colleagues.
I don't believe Star Trek was ever supposed to be about a hero's journey (that's Star Wars). The way I see it, it's an ensemble show.
I don't think the two are mutually exclusive. Sure,
Star Wars fits Campbell's classic myth structure, but the hero has friends and mentors who help him on his journey. If you call the series
Enterprise one journey, Archer would be the "hero," the main protagonist.
And since this was a TV show, different characters could take turns being the "hero" of separate storylines or episodes. Travis was the hero of "Horizon," Phlox was the hero of "Doctor's Orders," and so on.