Meh. It's just like anything else. You wouldn't leave your product unprotected if you worked in a jewelry store. You wouldn't leave your credit card info out where anybody could view it. You wouldn't leave your keys in your car. Why then would you be so carefree with 2-3+ months of your own hard work? It's a cut throat world. People will use you as a stepping stone if you give them the chance.
I'm certain that the best writers in the world seek out every single option available for protecting their work. At the very least, I will have that in common with them.
What you say is true -- but it's important for a beginner to recognize (and many do not) the actual value of what they have created.
In this respect, the previous poster is accurate, in that many beginning writers tend to wildly over-estimate the quality, and thus the desirability (the stealability) of what they have written.
Back when I was working in development -- when my job was to look for material, I remember getting a call from a writer -- anyway, someone who wanted to be a writer and he told me that he had a screenplay that he wanted to send to us (and by the way, the fact that he was even able to reach me and have that conversation was pretty unusual in this business) -- so I asked him, "Well, could you tell me something about the script?"
And he said, "I'd rather not."
That is -- he wanted it to send it to us -- but he didn't want to tell me what the script was about.
So I said, "Well, thanks anyway, but --"
And he was actually confused. He didn't understand why I -- first, wouldn't want to read his script without having any idea what it was about and, second, why I wouldn't want to be in business with a complete fucking nut -- which he clearly was.
So the point is this -- you copyright your material and then you have to go out with it.
Now, can it get stolen?
To answer that question, you have to understand the way in which intellectual property, like a screenplay can be owned.
You can't own it the way you own a lawnmower, like physical property.
Copyright law dicates what, specifically, can be owned, in the sense of being copyrightable.
What can't be owned -- are ideas. The "idea" -- the premise of your story cannot be owned -- only it's execution in a fixed form.
Like -- A great white shark attacks a New England Resort Community.
Nobody owns that. You want to write a screenplay about that? A book? Make a movie about it? Go ahead. It's yours.
After Jaws a bunch of people did.
Only a particular execution of that idea can be copyrighted.
So no matter what you do, you can't stop people from "stealing" your idea -- because you don't own it, legally.
Only it's execution, as embodied in your script. So that execution, as well as the idea, had better be great.
NMS