On a site and forum that is supposedly open and mature why is it that threads and posts seem to “disappear”, particularly those that challenge the “authority”?

I read a thread yesterday afternoon that was very well thought out and versed concerning differing measures of “punishment” by mods here and within a matter of minutes the thread had vanished and cannot be found.

Why is there such censorship on a site that professes liberalism and freedom? This seems to me to be a double standard..