We should be protecting them from birth, attitudes are everything. And this, anyway, is not doing that- this is about consent, not age. Surely, a 17 year old getting married of her own volition, is not a concern like an 18 year old in an arranged marriage.
They are focusing on the wrong things here. And many of those reasons are "tradition". From wanting women to be paired off with "suitable" partners, to having children, to controlling wealth, to total ingrained "free choice". The only difference is the degree of control and who by. No need for any of it.