We're seeing a wide trend in the US where people want rules to prevent people from making choices that they don't agree with, which was basically the opposite of the point of the US.
What if a host wanted to turn away somebody who was an avid white supremacist? This isn't the same thing as giving somebody a key to a hotel room.
EDIT: Worth pointing to another comment that cites the law: https://news.ycombinator.com/item?id=12453577
> Those anti-discrimination laws don't apply to hosts' private homes or bedrooms.[1] Paraphrase of law: "All persons shall be entitled ..., and accommodations of any place of public accommodation,..., without discrimination ... other than ... a building which contains not more than five rooms for rent ... which is actually occupied by the proprietor ... as his residence"