By now everyone who wanted has seen the ending of Lost's current season which I enjoyed, I was only bothered by the strange logic of their actions.
Locke said to Jack he would have to lie to protect the Island. Jack did persuade the others to lie, but not to protect the island, rather to protect their friends who they had left behind.
But what kind of protection is this?
Widmore surely won't give up the search just because his men didn't return (Jack doesn't know anything we know from the flash-forwards). It should just add to this suspicion that something was not right, so he will send an other search party which can hunt for the island undisturbed, because the Oceanic 6 didn't blow his story with the false plane at the bottom of the ocean.
So the Oceanic 6 has thrown their friends to the mercy of the man, instead of protecting them from him.
Because they could also use the world-wide attention they get due to their appearance and tell the whole world the plane was planted there. Governments cannot ignore their statements, because it concerns stealing enough dead bodies to fill a plane at the bottom of the ocean. Surely, the false plane cannot be a perfect replica which a serious investigation would discover. Also, the number of the bodies wouldn't be right, since Oceanic 6 shouldn't be on the plane which the creators of the false scene could not take into account.
Consequently, the statements of Oceanic 6 could easily be proven, and a large-scale rescue effort could be organized to find the island and the people left on it.
This rescue effort (in which the government would also take part, since it's a conspiracy involving stealing bodies) would surely hamper Widmore's plans which he could not follow undisturbed.
It's also possible the false plane could be traced to him, so he should have answer a few uncomfortable questions.
So the whole lying-the-world-to-protect-our-friend scheme by Oceanic 6 doesn't make sense. Surprisingly, the others in the group give in very easily to Jack's stupid idea and are willing to take a part in it.
This plot device was very unpolished compared to the effort the creators put into creating the mitology surrounding the island. Didn't they have enough time to think it over?