It isn't an illegal blockade, it is a legal one .
The U.N says.......................
"The United Nations itself, in the Secretary-General’s Panel of Inquiry report of 2011 concerning the Mavi Marmara incident from the previous year, found that Israel’s Gaza blockade is legal under international law. “Israel faces a real threat to its security from militant groups in Gaza,” determined the UN inquiry, headed by Sir Geoffrey Palmer, the former Prime Minister of New Zealand. “The naval blockade was imposed as a legitimate security measure in order to prevent weapons from entering Gaza by sea and its implementation complied with the requirements of international law."
https://unwatch.org/item-7/claim/claim-6-israels-blockade-of-gaza-is-illegal/