The Logical Atheist

The Jewish festival of Passover starts at sundown today. Is this the holiday that praises Yahweh for repeatedly "harden[ing] Pharaoh's heart" in order to change his mind about freeing the enslaved Israelites?  Or is it the holiday that praises Yahweh for inflicting collective punishment on all  Egyptians through the horrible ten plagues, culminating in the smiting of every firstborn Egyptian? ( Exodus 11:4-7  - "And Moses said: 'Thus saith HaShem [The Name; that is, Yahweh, which you're not supposed to say]: About midnight will I go out into the midst of Egypt; and all the first-born in the land of Egypt shall die, from the first-born of Pharaoh that sitteth upon his throne, even unto the first-born of the maid-servant that is behind the mill; and all the first-born of cattle. And there shall be a great cry throughout all the land of Egypt, such as there hath been none like it, nor shall be like it any more.    But against any of the children of Israel shal...

Why would Yahweh demand that "his chosen people" celebrate his repeated brutal collective punishment of the Egyptians (the 10 plagues), including his killing of all firstborns, even infants, especially when he himself admits that eight times he "hardened Pharaoh's heart" after Pharaoh promised to let the Israelites go, and Yahweh did this just so he could display his awesome power? (Hint: he's a narcissistic, megalomaniacal psychopath?)

Why would an omnibenevolent God repeatedly harm and kill innocent people via collective punishment, such as the great flood, the terrifying destruction of Sodom and Gomorrah, the 10 plagues in Egypt, and the bloody conquest of Canaan?