I resent and reject the argument that stories with happy endings are not realistic. I resent and reject the idea than in order for a story to be realistic or have traces of "realism" that a story must end sadly or ambiguously or tragically. I resent and reject the idea that stories have to be sad and tragic because life is sad and tragic. I resent and reject the idea that because the characters in a story get a happy ending and get what they want that automatically makes them irrelevant or unattainable or unlikeable.
Life isn't all one big, miserable tragedy, despite what Thomas Hardy believed. A happy ending doesn't nullify a story. It doesn't render the characters two-dimensional. It doesn't demean the story or the reader.
Life can be happy. An individual life has both happy and sad moments. Tragedy and loss. Love and gain. Ups and downs. It isn't all one or the other. One phase or stage may end in tragedy (family members die, lovers leave, you get fired), but that's not necessarily the end of the book--just that chapter. Other chapters are happy and hopeful and fun (you make friends, you find a new love,start a successful business). Shit happens. Sometimes it sucks, sometimes you want to bash your head into a wall, and other times you want to grin like an idiot.
Books with happy endings can contain all the same realism as books that end tragically. Books with happy endings can elicit all the same emotions and feelings as books that end tragically. Characters who get their happy endings can be just as relevant and relateable as characters whose lives are torn to shreds by "realism" and tragedy. I don't need to cry or feel despair or angst to be able to relate to my characters.
What the hell is the goddamn point anyway, if the characters struggle and suffer and strive all through the book, and then at the very end, still fail? How does complete failure and tragedy better justify and validate their struggle and effort. How is that a better reward than a happy end?