Of course we all deserve punishment for our sins, but Pharoah’s sins were especially heinous. Similarly, I think it’s possible that God hardened the heart of Hitler when he decided to invade Yugoslavia to punish a popular revolt against his puppet government - instead of going directly to Russia - the very difference in timing that caused the Nazis to be trapped in the Russian winter that led to their demise. God let Hitler’s psychosis become a weapon against himself, much as Pharoah’s hardened heart with regard to the Hebrews.
We also have to keep in mind that God foresaw the choices that both Pharoah and Hitler would make with their free will, thus, the hardening of their hearts would not be an encouragement to sin, but a re-directing of their foreseen sin to an outcome that would become their just punishment, instead.
That doesn't give God any less of a right to do to people today what He did to Pharaoh.
We also have to keep in mind that God foresaw the choices that both Pharoah and Hitler would make with their free will, thus, the hardening of their hearts would not be an encouragement to sin
First, to say that God simply "foresaw" is a severe understatement to His abilities beyond our comprehension. Second, there is no greater moral authority than God. So if God tells someone to kill another (many instances in the Bible), then it is not a sin, because sin itself can be fairly comprehensively defined as taking God's authority for ourselves. Third, our "free will" is practically indefinable with respect to God. In the end, whatever matters that God holds us responsible for are what we are responsible for--even if God did millions of actions to influence ours with the knowledge of what we would do in every situation.