The "bad" part of the word "scaremongering" is the "mongering" part.
It's fine to be scared of things, and talking about scary things, but when you intentionally work to scare people for profit, that's a pretty shitty thing to do. At that point, you're no longer informing the public, you're trying to provoke a disproportionate and often irrational response for your own financial gain.
Isn’t it only a bad thing to do if the person has no reason to be scared? If there is a fire in the building, I want someone to tell me, not shut up because of a desire to avoid scaremongering.
It's pretty easy to tell people about a fire in the building without trying to make money in the process. That's what "mongering" means. Fearmongering means trying to make money by selling fear.
It is a fallacy however to assume that because someone is telling you something and getting paid to do so, that the being paid part is the only reason they are doing it. If you already believed that a car is the most valuable asset a person in America is likely to need, you would be more likely to become a car salesman than someone who is fundamentally opposed to the idea of cars. So the set of car salesmen is probably skewed toward the people who really believe in cars and would be preaching car stuff even if they weren’t paid to do it. But if you are passionate about something, and can get paid to do it, why would you not take it as your job, since it makes you more effective at doing the thing and also lets you do it full time.
It's fine to be scared of things, and talking about scary things, but when you intentionally work to scare people for profit, that's a pretty shitty thing to do. At that point, you're no longer informing the public, you're trying to provoke a disproportionate and often irrational response for your own financial gain.