Earlier quoted context omitted.
What do you find unserious in that statement about Israel?
Just that regardless of your political inclinations, you need to be extremely ignorant of the complexity of the situation in the Middle East to be able to make such clear cut statements about what's justifiable and what's not. Disclaimer: I live in Israel.
My nation did something very similar to the Native Americans more than a century ago, and it's now universally regarded as an atrocity.
Of course none of this means that suicide bombers are justified or that Israeli children are war criminals. The world is more complicated than that, as you say; whole generations of innocent Israelis have now grown up on that land, and no more deserve to be forcibly displaced than the original occupants did. But I've never heard a convincing justification as to why the occupation was morally justified in the first place, and it doesn't become more justified with time.