As the article says, there are a couple of cults succeeding the denounced cult, Aum Shinrikyo.
I guess why successors are allowed to launch the similar cults.
To make it simple, it's equivalent to the movement that German authority allow Nazis believers to launch new political groups.
Surely, it's important for democratic countries to respect individual opinions. But, Japan's authority should limit criminals' right to form a religious or political group until expiration of their imprisonment.