If someone's writing or ideas inspire you as an artist, that's good. It means you're searching for inspiration and taking advantage of it. When you take those ideas, do nothing to change them, then claim them as your own, that's bad.
If I write a sci-fi western, I can easily say I was inspired by Firefly and Cowboy Bebop, two of my favorite shows. But that doesn't mean I'm ripping off the ideas. Of course, if asked, I would admit that those two shows influenced some of the concepts I came up with, but it's all setting. Now, on the other hand, if I use similar character names, dialect and slang choices, and story arcs, that's where it gets dangerously close to plagiarism, if not blatant theft.
People who create art take pride in what they do. Many of the creators I've met get super excited over the concept that something they've created has inspired someone else to create something new (ish since there's nothing new, technically). Themes, settings, basic high concepts, those are building blocks found everywhere in fiction. When a writer gets an idea and runs with it, making it completely different from the work that inspired them, that's awesome.
I'm not a legal expert, and this isn't legal advice. All I can say is that, it's important to find inspiration and make something amazing. But make sure it's noticeably different from the original work. Story arcs shouldn't match up, character names and traits should be as different as possible, and putting the story in a new setting can go a long way toward making your project completely your own.
Tons of authors have done this over the years, inspired by Tolkien (Warcraft, Robert Jordan, Terry Brooks to name a few) or Star Trek (basically anyone who saw an episode of the show and then went on to write science fiction), and no one is accusing those authors of STEALING from anyone (at least that I know of off the top of my head). But that's because they saw the inspiration (a vast universe of creatures and powers and opportunities for stories to HAPPEN) and made something that they loved.
As we've said before, we don't know a lot of the details of any of the cases we've discussed on the show. We're not passing judgement on anyone who is getting accused of plagiarism. What we're saying, as Beyond the Trope, is that it's important to be careful. And respectful. It's the best way to create without worry.