When did "you cannot blow up goodies to get baddies" suddenly become a rule of war? The US killed at least 100,000 civilian Germans, and closer to 1,000,000 civilian Japanese in WWII bombings. 100's of 1000's in Vietnam. Hundreds of thousands between Iraq and Afghanistan. And as a reminder, none of those countries except AQ in Afghanistan ever murdered civilians in the US.
What Israel is doing right now in Gaza is what any democracy would do in the same circumstance. If you think the US or any other nation would respond to this attack differently, for any reason other than they didn't have the military capability to do so, then you're just not that aware of history. Your own country would handle this in roughly the same way. If Mexican cartels did something similar in the US, we'd be bombing every known cartel operating site in Mexico, regardless of proximity to civilians.
No, Israel cannot be judged on a double standard, with one rule applying to them and another, to everyone else in the world. It's rank hypocrisy. Israel is not just going to stand there and do nothing about an attack like this. Because that is the only alternative to attacks which inevitably kill civilians: doing nothing. Hamas thought this through. They knew that any Israeli response would endanger civilians and the hostages they kidnapped, and that Israel would be condemned for it by westerners who urge one standard of conduct for Israel and another for everyone else. They are succeeding.