Shipments can easily be inspected by Israel and are clearly no threat to Israel. They are however in conflict with Israel's policy of punishing the population of Gaza. One PR disaster after another (I am reminded of the Chomsky affair yesterday). Without justice there will never be peace. Somehow I think Israel is truly not interested in either. Now if you throw in the fanatical ideology of settling in "Judea and Samaria" then Israel is all for that.
U.S., allies conduct 31 air strikes in Syria and Iraq against ISIS militants (Reuters)
from the article: Israel to Europe: Stop your citizens from sailing to Gaza with aid