The Israeli Commandos had every right to do what they did. Under international maritime law, when a maritime blockade is in effect, no boats can enter the blockaded area, and any vessel that violates or attempts to violate a maritime blockade may be captured or even attacked under international law.
They were also quite right to have suspicions about the cargo. As the Vice President of the USA put it: "Look, you can argue whether Israel should have dropped people onto that ship or not and the – but the truth of the matter is, Israel has a right to know – they're at war with Hamas – has a right to know whether or not arms are being smuggled in."
The Aid was also organised by a group called Free Gaza. This is an umbrella group of the IHH, which is closely linked to Hamas and has been known to voice it's approval of Suicide bombing.
The following is from The Israel Project:
1. A maritime blockade is in effect off the coast of Gaza. Such blockade has been imposed, as Israel is currently in a state of armed conflict with the Hamas regime that controls Gaza, which has repeatedly bombed civilian targets in Israel with weapons that have been smuggled into Gaza via the sea.
2. Maritime blockades are a legitimate and recognized measure under international law that may be implemented as part of an armed conflict at sea.
3. A blockade may be imposed at sea, including in international waters, so long as it does not bar access to the ports and coasts of neutral states.
4. The naval manuals of several western countries, including the US and England recognize the maritime blockade as an effective naval measure and set forth the various criteria that make a blockade valid, including the requirement of give due notice of the existence of the blockade.
5. In this vein, it should be noted that Israel publicized the existence of the blockade and the precise coordinates of such by means of the accepted international professional maritime channels. Israel also provided appropriate notification to the affected governments and to the organizers of the Gaza protest flotilla. Moreover, in real time, the ships participating in the protest flotilla were warned repeatedly that a maritime blockade is in effect.
6. Here, it should be noted that under customary law, knowledge of the blockade may be presumed once a blockade has been declared and appropriate notification has been granted, as above.
7. Under international maritime law, when a maritime blockade is in effect, no boats can enter the blockaded area. That includes both civilian and enemy vessels.
8. A state may take action to enforce a blockade. Any vessel that violates or attempts to violate a maritime blockade may be captured or even attacked under international law. The US Commander's Handbook on the Law of Naval Operations sets forth that a vessel is considered to be in attempt to breach a blockade from the time the vessel leaves its port with the intention of evading the blockade.
9. Here we should note that the protesters indicated their clear intention to violate the blockade by means of written and oral statements. Moreover, the route of these vessels indicated their clear intention to violate the blockade in violation of international law.
10. Given the protesters explicit intention to violate the naval blockade, Israel exercised its right under international law to enforce the blockade. It should be noted that prior to undertaking enforcement measures, explicit warnings were relayed directly to the captains of the vessels, expressing Israel's intent to exercise its right to enforce the blockade.
11. Israel had attempted to take control of the vessels participating in the flotilla by peaceful means and in an orderly fashion in order to enforce the blockade. Given the large number of vessels participating in the flotilla, an operational decision was made to undertake measures to enforce the blockade a certain distance from the area of the blockade.
12. Israeli personnel attempting to enforce the blockade were met with violence by the protesters and acted in self defense to fend off such attacks.
