I do think Israel had a right to respond with the military force available to it, but it's going to be very hard to convince me that their approach of making Palestinians suffer deaths, hunger, displacement, etc. was much helpful in defeating Hamas. Even if you believe that Hamas militants or their equipment were in every single one of those bombed targets that caused civilian deaths, it doesn't seem the net result is going to move the needle in Israel's favor.
Let's play this out. Israel goes forward with some sort of ground operation, the Palestinians continue to suffer and everyday we will hear about Israeli aggression. They don't cooperate with Hamas so they begin to execute hostages. Israel retaliates with even more bombing and house to house combat that gets even more civilians killed. They eventually pull out because of the cost, operational burden, and lack of support back home and in the US. Displaced Gazans who lost friends, family, homes, and belongings come back to start their lives from zero. Everyone is poorer, angrier and hopeless. A generation of kids/teenagers are lost to these conditions and become vulnerable to joining Hamas (or whatever worse thing it becomes or replaces it) - sometimes this is forced. This new generation of jihadists continue to get financed, to spread hate, to intimidate Gazans into supporting them, to shoot rockets into Israel, and to plan their next big attack to try to outdo this one and avenge the massive losses they suffered. This starts all over again... did I miss something?