I do not disagree with you in that plants contain Boron and that the body needs it in small quanities!
But to say that a person may ingest it without any harm is just asking for trouble!
For as I mentioned it may be used to Kill ants !
It is also used in Fungicides and Pesticides etc, which just so happen to be for the purpose of Killing things!
Now "IF" you read where wikipedia mentioned that borax may be handled because of it's Low "TOXICITY", but they failed to mention "ANY" thing about what may take place when you mix this with different Acids!!!!!!!!!!!!!!!!!!
So, not all may be as simple as it may first appear to be as they may have lead you to believe!
This idea is about as bad as the idea that you may use chlorox to wash your clothes, or you may use Ammonia to wash them!
Yes , either may be used and may be safe, but "IF" you accidently mix these two together, then you better have a Hospital near by for you to get to quickly or you may end up dead!