Let's say a chemical X is used in baby food production. There are no studies that show that it is harmful, because no studies have been done yet. Many chemicals with similar structure have been shown to be harmful.
Scientifically speaking you would be correct to say that there is no evidence that chemical X is harmful. There is no way yet to accurately model the interaction of any chemical with your body without any actual experimentation. You can make an argument that chemical X might be harmful because similar chemicals are harmful, but that would not be science.
I would not buy that baby food with chemical X if given a choice. Best case I don't lose.
Finding conclusive evidence in science often takes lots of time to gather enough data because there are so many different variables to consider. So absence of evidence means a lot more when you have been looking for a long time and invested lots of resources.
I wouldn't say that's true, if chemicals with a similar structure are harmful then there's weak but real evidence that X is harmful too.
A common fallacy is that "absence of evidence is evidence of absence". For a government this might mean "There is no definite scientific evidence that substance X causes cancer, so we do not ban it.".