There are some stories that deserve a happy ending. But there are some stories where characters do not require one.
I was troubled by this season of Doctor Who. The showrunner was keen on giving two companion characters major send-offs. It was one of those "they deserved their moment in the limelight." But it does dilute the main character's role as a super-intelligent, time traveling alien who always viewed himself as above the more primitive human race.
Part of the problem was that after the Doctor's current companion, Clara, died because she tried to be as clever as the Doctor himself. That was a pretty solid finish for a character that really did not take a back seat in her last season. She did not play the secondary damsel in distress role; she was a co-worker in solving problems. But the show brought her back in a weird Time Lord trope of pulling her back a second before her death so she could further humanize the Doctor. I don't think that worked at all especially since Clara is no longer dead, and running around with another immortal in their very own time machine.
Then for the annual Christmas special, the Indiana Jonesian character, River Song, had her grand send-off. Again, this plot seemed too forced and out of character. The Doctor has always been cast as a loner who always needed an innocent human companion to balance his potentially unchecked desire to create chaos and destruction. To have one last caper is one thing; but to push the tangential story line that the Doctor and River Song were timelessly in love (even through a re-generation) further weakened the Doctor's character.
Did Clara and River Song require a happy ending? No. It would have been more powerful if they had bad or heroic endings since that would have been key points in the Doctor's future decision making process (wrestling with guilt, shame, loss).
This same type of forced happy ending put a sour taste in many fans. The final season was a mess of character show reel type plots. One example was the back story episode for Alpert. The only thing that episode did was add evidence that the island was not purgatory, but Hell.
LOST could have ended well at the end of Season 5. Yes, there would have been many loose ends not tied up - - - but that was said when the series finally concluded in the sideways church and then some more plot issues. Was the sideways post-death limbo just a device to force a happy ending for Jack? It would appear so, but it was not executed well because once Jack awakened, he did not seem very happy. More confused than happy.
Other characters, such as Ben, got a happier conclusion than they really deserved. Ben was an alleged mass murdering, abusive psychopath who really did not pay any penalty for his sins. Was that all immaterial when Ben got to choose to stay in the sideways existence to find his missing family life with Rousseau and Alex?
Kate was very happy to see Jack once she awakened from her island slumber. But that happiness was contrary to the reality of their past relationship. In the O6 world, Kate's relationship with Jack soured quickly. On the island, Kate chose Sawyer over Jack. When Jack was in the depths of alcohol/drug depression, Kate turned his back on him. And when Jack was injured on the island, Kate did not stay by his side but instead left the island with Sawyer. It made no sense for Kate to come back in the after life to be Jack's main love interest, his soul mate.
But then again, in the final scene two characters in the church apparently had no happy ending: Locke and Boone. They had no one special with them to share the next level of existence. Both died in the island time frame in brutal and senseless deaths. And in the subsequent story lines, they were not truly mourned by their friends. Was it enough just to have these two loners be a part of a larger group?
Fans probably like the idea of happy endings because they had invested so much time and thought into their favorite characters. But sometimes forced happy endings are the worst thing a show can do.