I'm not sure I see any practical difference between a government saying "we will block website X because we don't like it" and "we will block website X because we say that website X is illegal". For example if Iran blocks a website which is critical of the regime, do you consider it important whether such criticisms are against the law or not in Iran? I think most people would consider it censorship either way.
If you want to make gambling illegal, then make gambling illegal and then enforce that law. You don't need to resort to indirect measures that go beyond the law (e.g. by preventing me from merely viewing the odds on a gambling website).
