Post Apocalypse thinking...
In answer to the question: Would humans really be savage and brutal in a post-apocalypse scenario?
Humans in general are Not inherently good... what they (we) are is incredibly selfish.
Men especially... Even Myself if I want to be truthful about it...
Self Preservation and greed are two of our primary motives and these go hand in hand with our Sex drive impulses...
In a Post Apocalyptic Scenario like Mad Max, exists an Atheistic View of the world going through cataclysm with no God above and No Holy Spirit within to limit or to clean up the human act... and with no Religion to instill and maintain Moral Laws on the peoples hearts and minds literally anything is possible... So in the Scenario that we are talking about there is nothing at all to prevent mans worst character flaws from taking over... and in fact every type of encouragement for the worst things to begin happening.
Witness New Orleans in the aftermath of Hurricane Katrina.. Rape, Pillaging and general chaos ensued until Order was re-instituted and enforced from the outside.
Things might have gotten real ugly if the Government did not send in aid so rapidly... It was still Ugly.. don't get me wrong... but Not half as bad as it cold have been. And had that mob tried to march North into Mississippi... it would have been a blood bath... People in South Mississippi were already expecting it to happen and were prepared to barricade roads and fight in militias to protect their lands, homes and families.
Now imagine a EMP (Electro Magnetic pulse) Nuclear strike 200 miles over central USA.
It would shut down all electrical power and destroy the electrical devices over 2/3 of the United states...
Consider all Electricity cut off...
Consider the effects of No Communication whatsoever.
Consider that there would be No resupply of food resources for months. (Unlike the aftermath of H. Katrina where the Disaster Relief was almost immediately trucked in and Donations were sent from all over the country to help out....
Consider that the average family does not have enough food on the shelf to exist for more than 3-4 days and without Electricity would have no way to cook or refrigerate the food they did have.
When people get hungry enough they start doing strange things. when people get to a point of Pillaging and killing for food to survive... do you think they will stop short of committing Rape with anything they deem rape-able?
To tell you the truth... I think Road warrior and Book of Ely were pretty close... the only thing I think they fell short on was that Gasoline goes bad after about a year or so... it does not keep like other fuels might... so the idea of having motorbikes and gun ship like sand-rails is a bit far fetched... its just Hollywood..
I think it Would be more accurate to think on the lines of a few rich people riding horses... lots of people dead everywhere... bones drying in the sun and no one caring enough to bury them...
People would be working farms inside of Feudal Warlords fiefdoms... Walls would be built around strong food storage areas... and Gangs of rogues, would have to be fended off from time to time...
There would also be Individuals sneaking around trying to kill or steal enough to live on...
It would be a very Brutal time.
Actually there could be a space for some of what you are calling Post Apocalyptic timing before the actual Apocalypse is finished, because according to the Bible the Apocalyptic End actually takes Years to play out... and it is a time of wars, famine, lawlessness all over the world and a One world leader rising to prominence in the Middle East.
In fact if you Read Mark Chapter 13 you will get a pretty good picture of what those days will look like... and also consider that it says that if God did not cut that time short... there would be Nothing Left.
Its a Pretty Grimm thing to think on.
Better to make your peace with God now before that junk goes down...
and Hope for "the Blessed Hope"...
Which is that you will be found worthy to escape all of that when the Lord Jesus returns and calls his people to himself... right before he pours out his wrath on the rest of mankind.
Maranatha