As per your comment in the "how did I become a Miraculous fan", I've often wondered why people think the best way to get you to be a fan of what they like is to viciously attack what you love.
Being mean to someone isn't going to bring them around to your point of view, it's just going to make them hate what you want them to like.
Wouldn't a better approach be to talk up the positive points?
If you're being polite, someone is much more likely to consider your point of view.
The only idea I really have is that they don't want competition, that this franchise is bad because it's not my franchise and is taking potential fans away.
An analogy I heard once is that just because you're a dog person doesn't mean you can't like cats too.
And for me that is true, I prefer dogs, but a friendly cat is just as good a pet.
Being a fan of this franchise won't stop me from being a fan of this other franchise, provided it wins me as a fan.
That's all you can do really, make the suggestion and then leave the decision to me.
If I don't like it, then getting aggressive to force the issue isn't going to work.