I'd say Barclay had it hard-terribly poor at handling himself socially and was implied to be passed around by various ships who couldn't or wouldn't deal with his eccentricities. Despite being quite competent at his field he was just a failure socially and even by the end of Voyager was only really beginning to find his feet. I imagine his life was a hard one. As stated above Kira had it hard yet it's implied in the books she will replace Sisko as the emissary at some point(and if you watch the show closely there are hints she will go in this direction) so her future seems brighter.
Pretty much any random crewmember on board Captain Picard's Enterprise in the Next Gen movies. If you didn't get a sprained ankle or broken arm when the D crashed into Veridian III, then there was a good chance you got assimilated into the Borg (and possibly shot with a holographic tommygun), got set on fire or flung dozens of feet from your console after an isoletic burst, or you died when Picard rammed the damn ship into Shinzon's Scimitar. What a menace. (I jest, of course )
I would perhaps say those sentient holograms the Hirogen programmed in their training centers to get slaughtered over again and again, but then, they don't qualify as 'main characters'...
Somewhat off topic, not being main characters: What about the augmented children at the time of the Eugenics Wars? Note that to the precise Spock "alive" equals "unaccounted for" and presumably "accounted for" equals "dead". This certainly gives the impression that any superman or superwomen caught was instantly killed. And what about any superboys and supergirls who might have been alive during the Eugenics wars and survived the mass bombings that wiped out whole populations? Were they killed on sight or thrown into solitary confinement for life? Khan and 84 other persons were in suspended animation on the Botany Bay. This gives the impression that there were 42 men occupying the rest of the 72 functioning units, but it is certainly possible that they included some children. I fail to see the waste in putting Khan's people in a reorientation center. After being "reoriented" they could use their talents to be very useful and to gain wealth and prestige. It seems to me that the waste would be to send them to a primitive world to struggle to survive without making any contributions to wider society, something that countless billions of persons have done before. And Kirk only asks 2 out of 74 prisoners which fate they desire Where's the democracy in that? does Federation law recognize the other 72 augments as Khan's slaves? And the first prisoners at Australia's Botany Bay colony didn't go on to tame a continent all by themselves. They were later joined by many thousands of prisoners and free persons who went on to tame Australia. I'm not sure if 74 persons would be enough to found a viable colony on a strange new planet without any aide from outside for decades or centuries. In WOK 15 year's later Khan's few surviving people look like they are in their twenties. Maybe Khan's supermen and women aged much slower than normal people. Maybe they are the under-fifteen-years-old children of Khan's adult followers, kids who look older because being supermen they grow faster than normal humans. Or maybe they are aged between 20 and 30 like they look and were aged 5 to 15 on the Botany Bay. In any case, Khan's people have had a hellish time on Ceti Alpha V, and in the latter two cases they were kids for part or all of that suffering. Then the adult or teenage augments escape from their hell planet and are free and their crazy leaders gets them vaporized! Of course it is possible that the hundreds? of cadets and trainees aboard the Enterprise might have included some as young as the uncertain age of Khan's followers. Midshipman Peter Preston looked very small and young when I first saw him. Then I recognized Ike Eisenmann and decided he was old enough for Starfleet, if possibly too short. And then Vonda N. McIntyre's novelization and the script both say that Preston was fourteen years old. So I am uncertain whether the Enterprise rivals Khan's group for the title of having the youngest person killed in the movie. And then there is this: http://3.bp.blogspot.com/_of7mShM5N1g/SpfniPl9F-I/AAAAAAAAAKg/hF-ZvMOg02Q/s1600-h/khans_son.jpg https://www.trekbbs.com/threads/another-pic-surfaces-of-khans-baby-from-twok.102909/ But of course none of them are main characters in Star Trek or WOK.
That seems like a leap to me. "Unaccounted for" means just that. It means that they don't know what happened to them. When Spock says that 80 or 90 of the supermen were unaccounted for, it means that they could have escaped, they could be missing, or perhaps they were killed in the war, but there was no means of verifying their deaths. Presumably the ones that were positively accounted for were either dead or imprisoned.
I'm seriously torn between Seven of Nine and Tasha Yar. On the one hand, no matter how much horror Tasha, Kira Nerys, Ro Laren, and others had to live through, none of those characters have to live with the guilt or loss of identity Seven of Nine has. But on the other hand, Seven got a chance to reclaim her life, while poor Tasha was screwed over in TWO timelines, dying a "senseless death" twice. Oh, and being a "consort" to the Romulan who captured her means she was getting sexually assaulted AGAIN (after growing up with "rape gangs" on Turkana IV).
Those miners on Janus VI. You live in a space utopia but work in a mine. Your buddies get incinerated by a rock monster. And then you come to find out that YOU'RE the asshole.
That guy drilling the empty holes he’d kill to protect at the start of TFF. His life was a bit crummy, given the eradication of poverty throughout the federation. Where’d he go wrong?
What he did wrong was living on Nimbus III, the Planet of Galactic Peace, which apparently is in sort of a three way neutral zone between the Romulans, the Federation, and the Klingons. The Federation Ambassador said the three governments had hoodwinked a bunch of suckers from their worlds to settle there about 20 years ago. If he chose to leave a relatively utopian core world of the Federation for Nimbus III that decision was where he went wrong. If he decided to leave some relatively crapsack world in one of the three realms his decision was not so bad though still clearly a mistake. From what I saw of Nimbus III there was little probability he came from a world that was as bad or worse and so there was little probability that the decision to come was not a bad mistake.
What about "God" on Sha Ka Ree? Getting imprisoned for millennia behind the Great Barrier, being bored for all of creation, and the first people he meets, questions his credentials, gets Vulcan mind probed, and gets the shit blown out of him by a Klingon Bird of Prey.
How about Shinzon? He was Kylo Ren before Kylo Ren. And actually had a lifetime of abuse at the hands of Romulans to give his homicidal and rapey tendencies some level of understandability.
Odo had a lonely life as the only one of his kind for most of his life. He was experimented on in his early years and then had to work for the Cardassians which couldn't have been easy. Then he found where and who he came from only to realize that they were pretty horrible.
They put O'Brien through the mill. Then Picard, who got the borg treatment, the Cardassian treatment and misplaced his heart. That's tough. He also loses a bunch of relatives he's close to. He doesn't age too well in AGT either.
Tuvix - he came out of the transporter to looks of scorn and disdain, with everybody he knew and loved looking at him like a monster. Then Captain Janeway sentences him to death over his objections.