That's how science works though. You formulate a hypothesis based on current understanding of the subject matter, then when evidence presents itself the hypothesis will either be supported or rejected. Then the cycle repeats itself. There's no way around it. You can't get facts without evidence, so until evidence is found you can only make assumptions based on what is already known.
With regards to COVID-19, it's a novel strain of virus. Hence, we don't know anything about it except what can be deduced from our knowledge of other viruses. This includes modes of transmission, symptoms, treatments, etc. Rather than just saying "we don't know" when asked about it, scientists can instead say "we don't know, but based on our understanding of other infectious viruses, we think that.......", which is much better.
And when it comes to infectious disease, there's no black and white answer. Some people get infected but don't show symptoms, some people get infected but show different severity to others, some people recover but get reinfected while others don't. So you see, even if we wanted to give direct and consistent answers, we couldn't because sometimes, the world is just inconsistent. The best we can do is give probabilities, which is why all science revolves around confidence intervals. It's like they say in Star Wars: Only a Sith deals in absolutes.
Science is only "wrong" once proven wrong. Until then, it's just the scientific method.