I know this will probs gather a lot of controversy but please read thoroughly before you come after me or something.
I've been doing fan art and making up fan fic stories since I was like 8 and obsessed with Sailor Moon, but I didn't start writing until I was 13. It was a Harry Potter fan fic. It was a retelling of Order of the Phoenix, but focusing on a romance between Neville and an OC I made called Fabi. I had recently just discovered fan fiction, but didn't read a lot of OC works. I really just jumped in and went for it. Running at 214 pages (handwritten), the original is still probs one of my longer pieces, though. It was my first big writing project and the first story I'd ever finished; I was so proud of myself for actually finishing a story. Even then I had a penchant for starting something and not completing it. I put it down for a few years and then came back to it and made an important discovery:
The story was garbage and Fabi is what everyone would call a Mary Sue.
I didn't really know the term "Mary Sue" when I started writing. I created a character, gave her a backstory, gave her a personality, and was able to do whatever I wanted in-story with her. I had no fear of being criticized for making a "Mary Sue," mostly because I had no idea what one was.
However, once I returned to Fabi's story, I had found out what a Mary Sue was. This was during the height of anti-Mary Sue ideology being spread over the internet. So many pages were dedicated to conducting "Mary Sue" tests to see if your OC was one or not. Writers were TERRIFIED of creating a Mary Sue and being bullied by people because of it.
The thing is, Mary Sue went from being a literary criticism of character to a tool used by bullies to harass writers and instill fear that their OC may never be "good enough." Loads of writers have a fear of their characters being insulted like this; the internet has equated Mary Sue to worst, most horribly written character of all time.
It's true some OCs may not be well-written, but how does being a Mary Sue harm someone? What does someone else's fun do to hurt you? Why call someone's OC a Mary Sue instead of offering specific constructive criticism? What does even calling someone's OC a Mary Sue do besides cause someone else pain?
We as a community need to stop slinging Mary Sue around like a loaded pistol. Using Mary Sue as criticism is no longer effective and it does far more damage than help. We need to start giving encouraging, polite constructive criticism. We aren't rivals here. We're all nerds who love our various pieces of media.
Writers learn a lot from self-exploration and experimenting. From writing Fabi's story, I learned a lot about writing even though I came to hate the story I wrote a decade ago. I learned what worked and what didn't. I grew up with my work and revised, revised, revised. Learning what made Mary Sues "bad" (honestly, just cliches and some other things) did help me grow as a writer, but having your characters be called a "Mary Sue" helps no one because it doesn't explain anything. It's just an insult. Calling characters a Mary Sue is not valid criticism and it only spurs writers resenting the commenter or worse, growing to hate their own work.
And it's not just a useless piece of criticism. The idea of what's "well-written" and not is super subjective. There's always going to be one person who hates your work and thinks everything sucks. Likes and dislikes are not the same across the board and the same goes for criticisms. Honestly, there are Mary Sue tropes that don't bother me at all. Whether I think they're pulled off well or not if debatable. But I admit I'm a lot more lenient on this kind of thing in fics. I'm more than willing to go with the flow but a lot of my watchers know my big thing I do point out to other writers is grammar and spellings and such.
But anyway. The fear of Mary Sues only hurts writers and forces their work into smaller creative holes. What's well-written is up for debate and yes, you can leave polite criticisms for a writer, but using the threat of a Mary Sue is no longer acceptable and needs to be tossed out. Writers, especially young writers, need to be allowed to write and have fun and experiment without fear of bullying. This isn't a piece on like banning criticism; I'm only asking for people to reconsider using Mary Sues as a threat and insult. Writers do need criticism to grow, but we as writers and readers need to start offering better advice to others in our community. And in this day and age, calling an OC a Mary Sue is simply not acceptable.
So I say go ahead: write a Mary Sue! Have fun with your work and explore all possibilities! Go wild! Write what you want and experiment! You will find what works and what doesn't. Writers, you are allowed to have fun and create characters as you want. At the end of the day, only you get to decide what stays published. Listen to criticism, but take anyone who cries "Mary Sue" with a grain of salt.