Timeline:
1.On 12Jun14 the 3 teens were kidnapped and murdered.
2.Israeli cops start looking for the asshats/and start rounding up bad guys they let go in the Gilad Shalit "deal".
3.meanwhile, there had been rockets out of Gaza everyday (save 5 days, 80 rockets on 1 July was the high mark) between the kidnapping and the Israeli response which came on....
4.8Jul14 the sh**t hit the fan
As you yourself pointed out, the Israeli government used the kidnapping as an excuse to renege on the Gilad Shalit "deal" by rounding up everyone they wanted to lock away without a key under the pretense of it being police work. And then they were shocked, shocked I tell you, that Hamas retaliated by the only means they had.
Now I agree that the Gilad Shalit "deal" was a bad one, but that doesn't affect the facts concerning the kidnapping.
What's worse, rounding up a coupe hundred bad guys or killing 3 civilians hiking? What's worse, rounding up a couple hundred bad guys or launching hundreds of rockets at civilians?