Goldstone, for example, said that the UN report he wrote "in no way contradicts the right of Israel to defend itself." He just wrote it in such a way that so severely hampers Israel's ability to defend itself as to make the words meaningless.
Amnesty International's Middle East director says that “Israel has a legitimate right to defend itself from rocket attacks but this blockade is not the right policy."
Human Rights Watch writes that it "recognizes Israel's right to defend itself against attacks by Palestinian armed groups in Gaza...But lawful means of self-defense do not include harming civilians in Gaza." (Note they do not say "purposeful" harming of civilians, they are implying any harming of civilians, even if Geneva allows it.)
The EU Parliament passed a resolution last year that stated, in part, that it "Reaffirms the right of Israel to defend itself, but stresses that this right must be proportional to the threat received and should be exerted in full compliance with the humanitarian law and..... " a full paragraph of what Israel is not allowed to do even as they assert this "right."
The upshot seems to be that everyone agrees that Israel is certainly allowed to defend itself in theory, but there is always a "but": Israel has no practical, legal, moral means to do so according to these self-proclaimed arbiters of law and morality.
The Mabhouh assassination, presumably done by Israel's Mossad, is a textbook example of this rule at work. Assuming that it was done by Israel, here we see the elimination of a known terrorist and murderer; who was in the process of procuring weapons meant to murder Israeli civilians. No civilians were killed or injured; there was no bloody mess for the chambermaids to clean up; no one else in the hotel were even woken up from their sleep - this was the cleanest, quietest way for Israel to defend itself.
And yet, the world is up in arms, mostly because it appears that passports were forged!
From Al-Arabiya:
European Union foreign ministers condemned on Monday the use of forged European passports by assassins who killed a a top Hamas figure in Dubai, but made no direct reference to Israel.
"We strongly condemn the use of fraudulent EU member states' passports and credit cards acquired through the theft of EU citizens' identities," the foreign ministers said in a statement drawn up during a meeting in Brussels
The EU also for the first time condemned the act of assassination in Dubai believed to be carried out by Israeli spy agency Mossad.
Luxembourg Foreign Minister Jean Asselborn said the culprits must be punished, stressing that such political assassinations "have no place in the 21st century."
Even though Goldstone ridiculously asserted that Israel could somehow eliminate the rocket threat through "commando actions" - showing his extreme ignorance of what the threat even was - apparently the clean assassination of a terrorist scumbag in Dubai is not an appropriate way to approach that very same threat. After all, the killing of Mabhouh was much cleaner than any actions Israel could do in Gaza - no damage to anyone's houses, no unwanted injuries, no danger to innocents. And yet it is condemned.
(It will be recalled that Mabhouh's often used forged passports as well, and no one seems to be very worked up about that.)
Putting it all together, and Israel's critics still cannot come up with a single realistic scenario of how Israel can legally defend itself, even as they insist that Israel has that "right." Having the right without the practical ability means that, according to these people, Israel really doesn't have the right to defend itself.
They might as well just admit it.