This source specifically says that they don't know. How did you use "we don't know" as "we know?" All it says is that they have not determined the right amount, not that there isn't a safe amount or even that some isn't better than none.
"There is no known safe amount of alcohol use during pregnancy or while trying to get pregnant. There is also no safe time during pregnancy to drink. All types of alcohol are equally harmful, including all wines and beer. When a pregnant woman drinks alcohol, so does her baby." - hint, 2nd and 3rd sentence.
None of that, literally not one word of it, says that they know that alcohol is bad (we don't need to keep saying "in proper quantities" unless someone truly things that water needs a warning, too). You are letting them "lead you" with the writing style.
Read it careful. All it says is that "they don't know." They never say alcohol is dangerous. They point out obvious things and let you draw false conclusions. This is standard marketing techniques that we talk about regularly. How sales people state something simple and true that tells you nothing, and let you presume that they meant something more.
This is how you get people to lie to themselves, it's what prevents lawsuits and you never have to say things as people will "fill in the gaps" with their own assumptions.
You read this and think they just said alcohol is known to be bad. I read it and see words that very clearly say "we don't know much of anything."
Seriously? Do you only read what you want to read? All alcohol are equally harmful - does that sound they never say alcohol is dangerous?