How is that different from a hosting provider that has to address legal complaints regarding spam, copyright infringement, etc. on their servers? Just like a hosting provider, they specifically have a relationship with the website owner to provide the reverse proxy service. It's not like they can say "we don't know who or how our service is being used".

It seems to me that if they want to be in this business they have to deal with these liabilities and complications, not hide behind some vague "our hands are tied" language.