A couple of reasons.

1: I can. It’s fiction, these characters are not real people, and if I wanna torture them I can do so without bringing harm to a real human being; discomfort is not harm, if you don’t like what I write/draw, fucking block me like a sensible adult, or get off the internet if you’re so young you need someone else to curate your online experience for you. I’m not your parents; I’m a random stranger on the internet.

and

2: To cope. With a lot of different things. I was groomed, molested, and raped as a child, and writing about similar things in fiction helps me to process. Posting it helps other people who might not be as creatively inclined to process as well; I know this because I had countless people tell me my writing helps them cope and/or process. And also Group Therapy is a thing.

I also suffer from deeply disturbing and violent intrusive thoughts. Antis are so worried about fiction turning people into predators that they never stop to consider a lack of a fictional outlet would probably turn me into a murderer.

So honestly, which would you rather? I write some fucked up fiction about cartoon characters, or I let the intrusive thoughts win and bludgeon my coworker to death with a lead pipe? 🙂