I'm no fan of this act but your characterisation is highly misleading.
To pick two examples from the document you linked:
Discussion of being a sex worker would not be covered. The only illegal content relating to sex work would be if you were actively soliciting or pimping. From the document:
* Causing or inciting prostitution for gain offence
* Controlling a prostitute for gain offence
Similarly, discussion of drug use wouldn't be illegal either per se, only using the forum to buy or sell drugs or to actively encourage others to use drugs:
* The unlawful supply, offer to supply, of controlled drugs
* The unlawful supply, or offer to supply, of articles for administering or preparing controlled drugs
* The supply, or offer to supply, of psychoactive substances
* Inciting any offence under the Misuse of Drugs Act 1971
That's very different to criminalising content where you talk about being (or visiting) a prostitute, or mention past or current drug use. Those things would all still be legal content.