I think you're probably right, lots of people probably don't realise how many babies are saved by this.
But that doesn't excuse the unnecessary risk of giving it to women who don't need it. And yes, midwives insist that women have it even if the Father is -ve. Presumably in case the Mother is uncertain who the Father is.
I know this from personal experience and also know that some midwives are uncomfortable with this. Esp as the practice of giving it during pregnancy as well as after labour is relatively new.