As an alter based on a fictional character, I personally don't like the term "fictive" being used to describe me because I feel that it's important that I recognize that I am not a character, I am a person. However, I will never tell anyone else they cannot use the term "fictive" because I don't like it, because it's not healthy for me to view myself as a fictive as opposed to just an alter. For some people, including some fictives in my system, that is a healthy way for them to categorize their identity.
The problem here is that every time I try to express my own dislike for being called a fictive, I get flocked by people who think that no one should ever use the term because it "encourages delusions" or whatever (which itself plays into an ableist view of delusions as this evil that must be shut down at every corner by everyone) or promotes unhealthy coping mechanisms. I wish people could understand I'm talking about me, not everyone.
Conclusion: I'm an alter based on a fictional character, please don't call me a fictive. But if you're a fictive, call yourself a fictive! That's great. I'm /gen so happy that there's a word and community for your experience. I wish people didn't see every personal preference as some all or nothing statement.
Shadow the Hedgehog (MPC, if you need to use fictive for tagging purposes, I won't be offended. Otherwise, if you could maybe use a tag like "shadow the hedgehog alter" I'd love that)