Writing is tough. Getting published is tough. Finding an audience after you've been published, even by a large imprint, is still really tough too. I know I keep writing despite all of that because it's how I express how I experience the world, but also because it's so satisfying when even a single person reads your work and says they gained something from it. I'm still chasing that elusive writing career, but I think the only way to stay sane is to hang on to the positive feedback from people you trust and know.
Off topic question: Do you use writing or organizing software?
I use Scrivener for larger projects. I can't live without it anymore because it makes editing waaaay easier.
What is your opinion about writing for free? Is it just for practice and do you think it might help promote you as an author, or do you think its not a good idea? What about fan fiction?
I think fan fiction is for fans and should be free, not only because of copyright laws, but also because I view fan fiction as a collective endeavour. As someone who's been writing non-fiction for free for five years I can say, based on my own experience, that it doesn't really promote you as an author. What promotes your fiction is your fiction -- which isn't to say that non-fiction doesn't have a role for promoting your personal brand, but it just isn't the same thing.
Most professional writers will tell you that publishing something for free is bad for business, because it devalues your work and the work of others. Writing is work (except when it isn't!) and you should get paid for it like for any work. Visibility doesn't pay the bills, just like having a gazillion social media followers won't pay your bills either.
This doesn't take into account that sometimes it's worth putting your work out there to get feedback, or to support a cause, or to share a thing with friends. But if you're publishing with the intention of building a career, you need to submit to places with an established audience, and those places (online magazines for example if we're talking short pieces) will pay you for it, even if it's a rather small sum. The standard rate, as far as I know, is six cents a word, which adds up to a couple of hundred dollars for an essay or a short story, but I also know of tiny magazines where fifty dollars is fair.
Nowadays you can of course self-publish. If you're able to build an audience, you can make a living selling your writing through Amazon or Patreon. Patreon is a fascinating business model in the sense that it's basically pay what you want, which also means you can publish your work for free and let others decide what they think it's worth.
I gave up on trying to make money. The market is bad for Science Fiction Writers, and it is shot through with graft. Now I write because I must. I wouldn't dare write non-fiction because someone might follow my advice, and we mustn't have that!
Perhaps I blog about Religion and the search for legitimacy because I am trying to find an escape clause?
I have a hard time believing the market is bad for SF, considering we're currently seeing a huge uptick in TV and movies that fall within the genre. We've seen some amazing literature recently, like N.K. Jemisin's Broken Earth series. I won't claim it's easy to break through in the genre because the competition is fierce, but I'd hate for you to give up on it because of a perceived lack of readership.
Sometimes I think about grabbing a book nobody has read for a long time, changing the names of people and events, reworking a few scenarios and then selling it. Is that terrible or what?
How could I think of such a thing, and then what if nobody realized and started buying it? Then I'd be a truly lowdown rotten scumbag with lots of money, wouldn't I? I'd be worse than Disney. Before you know it I'd have my own theme park. That would be just awful.
Sherlock Holmes is now in the public domain, so you're now free to publish your own detective stories if you feel so inclined