Freedom of speech is not a worldwide thing. There are parts of the world where you can’t speak your mind and if you do you get jailed or killed. Your client is/was free to speak his mind but the mods have the right to ban you if your views and actions are a detriment to the site, and you’d have a better argument if EVERYONE was in disagreement with his banning, but his views were deemed detrimental enough that it warranted his banning. There are consequences for said freedom of speech, it doesn’t shield you from punishment, see Roseanne.