(Sigh)
The thread is only a "derail" if someone believes the purpose of some of those replying was to discuss the Mavi Marmara attack. In reality the purpose is just to blame Israel for something, so we get the usual conspiracy theory "logic" in these threads:
"Let's talk about the Marmara attack."
"It proves Israel is evil!"
"Actually, the claims of those on the ship are clearly unreliable and prove nothing like that."
"Er.... never mind! Israel is evil anyway!"
This is why these threads keep moving through the usual list of "proofs of Israeli evil", no matter what their starting point is. Since most of their "proofs" prove nothing of the sort (e.g., Israeli immigration policy is practically the same as that of many other countries, Israel's reaction to years of bombings by Hamas was, if anything, far more moderate than any other country would have done, etc.), and those who do show Israel does wrong -- which is sometimes does -- hardly justify the insensate hatred of Israel they clearly exhibit, the threads keep moving from one false or underwhelming "proof of Israeli evil" to the next.
These threads are so long since they keep telling the same lies about Israel again and again, and thus need to be corrected again and again.
But it's a pointless excercise. The best thing to do, which will be my policy from now on, is to simply abandon the thread once the usual gang shifts the subject from the point of the thread to "look, here's some other reason Israel is evil!" territory.