@jerrybanfield, you have too many questions to be answered. Each of these questions need a blog or 2 to cover them. I would start by giving my 2 cents opinion to the first question(s):

Why do we think life would be better if everyone agreed with us? Why do we get mad when people disagree with us?

We can see this phenomena in everyday life as well as in all wars and religious, race, color, gender and whatever you can come up with fights.
One the most amazing books in psychology I read were written by Dr. David Hawkins, who made the map (levels) of consciousness

Since I came across this map, my understanding of human behaviors (myself included) increased drastically. With understanding comes empathy and the ability to change ourselves and make a positive difference in the world.

As you can see, this map divides the human emotions (consciousness) into positive and negative energy. Usually negative feelings come in package of 2 or more, but never alone.

For example, when we require others to agree with our opinion and they don't, feelings of anger, pride, desire, fear and shame comes to the forefront. How? Well, the fact that we want others to agree with us is because of our desire to be correct or right in what we say because our pride is on stake because we fear that if we are wrong then we will lose face (pride), which makes us angry when someone doesn't agree with use because they just did what we feared, they made us look wrong, which makes us feel shame and hurts our pride. How could they?

Crossing the distance from negative to positive requires a lot of energy and courage. That is why courage is the factor that divides the positive from negative. Because if we are at the level of courage, then we will
1- Be able to bravely admit and accept that we can be wrong and that is okay.
2- We will understand that we should accept and respect differences and that being or having different opinion, doesn't necessarily make us wrong or right.
3- We will start listening to others' opinions and maybe learn to think in a broader way and grow wiser from these interactions.

I hope you find this helpful :)

Love and peace :D