I think you misunderstand risk. Whilst any assessment should be based on known facts, risk it's inherently uncertain; if you know something will happen, that's a certainty, rather than a risk. If you know someone may pose a risk, then there is a risk i.e. a chance that the harm will materialise. Knowing there's a risk is not the same as knowing it will manifest. And, yes, that does mean we all present a risk; it's a matter of assessing the extent of it (based on what we do know, which, can almost never be the whole picture).