The remedy in that case then would not be a tax but to ban them from operating in that country. We already have these sorts of export controls with other countries. It is just the case that despite their egregious human rights record (bone saw, anyone?) the United States has propped up the Saudi regime since basically it first came to exist roughly a century ago.
The reason is obvious - Saudi brutality is a feature not a bug. It secures access to cheap oil.