1- Right to defend? Sure. Right to offense? No. Bombing hospitals, UN camps, unarmed civilians, and even the locations that Israel demanded the civilians to escape to prior to bombing being bombed shortly afterwards is in no case a self defense.
2- There is no proof of Hamas committing Mass-Murder, Beheadings, Rape, Abduction, Ethnic Cleansing. Rather all of it was committed by Israel which has been proven by several sources, including Israel themselves. Israeli politicians have time and time again expressed their intent to commit genocide several times to the Media.
3- To say that everything kicked off on 7th of October is illogical. Israel has been causing far more terrorizing attacks almost on daily basis, with far wider casualties on Palestinians side instead of what Hamas does. Check the stats from official UN website, especially the year of 2014, and you’ll notice this has been going on for a really long time. If anything, its Hamas that has a right to claim self defense, not Israel.