Earlier quoted context omitted.
TPB never supported absolute free speech. I can't find it now, but they used to have a section of their site where they posted responses to media company lawyers, and they basically said they wouldn't take down anything except child porn. I'm not sure if the rules have changed in the years since.
CP is one of the very few things where mere possession is illegal. It makes sense that TPB, which is mainly against copyright and IP, would not allow it.
AFAIK this is not an absolute, global truth. IANAL, but I do know the stance on CP (e.g. anime, ages of wedding, written-Lolita- etc differ per region. Legal and cultural).
In many countries, possession of certain books is illegal. Possession of blueprints of weapons is illegal and so on.
Point being: banning CP is still a moral choice, made by the operators of the site, not some absolute, global common baseline.