Not really. Blocking of illegal content is possible -- and can be (and, at times, has been) encouraged and even mandated by government -- even without protection of legal content. So, while the qualifier might suggest that such practices would not be curtailed by the neutrality, they don't provide the basis for more invasive monitoring and control than the absence of neutrality does, because the basis of that more invasive monitory and control already exists in the illegality of certain content, whether or not there is neutrality for legal content.
Why would the statement need to provide any basis? It's merely a carefully worded expression of a decision that's already been made. You will find even recent history rife with examples.
