It is not Israel's action, but the vitriolic reaction to it that has been disproportionate. There's only one explanation: antisemitism.
This article illustrates the mind set of Israel's supporters. IN their view, no reasonable human being could ever possibly object to what Israel is doing in Gaza, i.e. breaking the cease fire, blaming HAMAS (the elected government) and invading. Therefore, since all reasonable people love Israel and never criticize her, all criticism of Israel is ... anti-Semitism.
Anti-Semitism is hating people because of what they are.
But we can justly criticize Israel for what it DOES.
Defending Israel with the excuse "it's just anti-Semitism" is like defending Hitler by claiming he is the victim of anti-Arianism!
You might want to read the comments to this article as well (while they are still there).