This is a quotation, often said to be from Voltaire. It is, in fact, from S. G. Tallentyre, 'Friends of Voltaire' which was published in 1907.
'I disapprove of what you say, but I will defend to the death your right to say it.'
Article 18 of the Universal Declaration of Human Rights states that: 'Everyone has the right to freedom of thought, conscience and religion.' (Or, presumably, to have no religion).
When I was working in a centre for asylum seekers, with people of all colours, ethnicities and religions, a white European Muslim (ex- Yugoslavia) said to me 'I'm racist. That's the way I am.'
My reply was, 'I don't agree with you, but since you don't make problems and simply avoid any social contact, then that is your right.'
Probably one of the nicest racists I've ever met. At least he was honest!