That's a fairly common question, actually, and probably deserves a post of its own. There's no true consensus, because there's always that miniscule chance that some jagoff will steal your work, but my personal philosophy is not to worry and not to care. As far as I'm concerned, the moment I share my world, my world is no longer mine--it's everybody's. I encourage people to play with it, take it, make it their own, make spin-offs and alterations, whatever. It would be high praise to me to see someone take something I've come up with and love it so much they have to do something with it themselves. Imitation is the most sincere form of flattery, as they say. I've never had a bad experience with being stolen from. People have before asked me if they could use something cool I came up with, and I said yes. Others have seen that I've posted similar ideas to theirs, and they've been disappointed that their idea isn't original, and want to change it. There's an instance where someone wanted to be original so badly they actively pushed away from an idea because they saw it elsewhere. Ultimately, I think that's the way a lot of people operate. Most people want to create wholly original stuff. Most people don't want to steal. When I was in high school, I wrote a short story and showed it to my best friend. He loved it so much he wrote a sequel. Then he showed both stories to a friend of his own, and she wrote a third piece to it. That was pretty awesome. I did not think one quick story could get so much attention, and breed so much more creativity. They took the original story and transformed it into something bigger and better. I always wonder why people worry so much about their stuff getting stolen. Don't people realize who awesome it feels?!
Having read your comment, I just realized that I grew up in the heyday of American capitalism, Wall Street heroes, everyone wanting to be rich, tons of popular movies about small town boys making it big on wall street, the American dream, mansions, expensive cars, flashy, wealth glorified. Intellectual property, copyrights, laying claim, possessing, security, investments, portfolio management... Then I saw that fall apart. For a while now I've been noticing the open-source movement gaining more and more traction, skill-sharing, young people growing up in a world in which people share freely, all content is accessible, and these younger people rebel against people who try to monetize greedily. Caught between multiple generations, I am. I am very pro open source and skill-sharing, but the older part in me instantly thinks about profit margins and intellectual property, especially considering I worked for years at law firms specializing in such things. It's a bit confusing.
Ah, the good ol' American Dream. I could philosophize on that for ages. We could turn this into a very different discussion... But to attempt to tackle this in a way that makes a semblance of sense, I'd just say forget about money. Worldbuilding, for me and for most, is a non-profit hobby. You do it for the fun and the joy of doing it, with no expectation of return on investment. The return I get is happiness when I learn someone enjoys something I've created. That's all the profit I need. Once you throw money out of the equation, perspective changes. How does one steal something you freely give? I did start this post by suggesting a goal and a basic "product" to shoot for, but don't let that be the motivating factor, just let that be a guidepost to steer the development of your world. The "product" is always simply a way to share the world you've created, not something to be sold and made money off. Think of worldbuilding as any other hobby, not as a means to an end. One does not go skydiving expecting to have sponsorships from Red Bull and GoPro; one goes skydiving because skydiving is fun. And besides, even if you absolutely do intend to make money off it, many people have made money by sharing freely first. Tarn Adams, creator of the game Dwarf Fortress, gives his always-in-progress game away for free, yet makes a living off donations. But I think of that as a bonus, not the end goal.
Read your entire comment understanding what you were saying about forgetting about profit, do it because you enjoy it. But, being a Wall Street fantasy baby, it just wasn't sinking in. Until the above quote. Then it clicked. Always nice when someone phrases a concept in just the right way that it clicks for you. One does not go skydiving expecting to have sponsorships from Red Bull and GoPro; one goes skydiving because skydiving is fun.