Why do people disagree on so many things?

People have many varied opinions on every topic you can think of. On YouTube for example, if you comment on something you agree with, you'll likely get someone passionately or even angrily disagreeing with you.

Why do people disagree on so many things? Let's explore that.

A simple statement such as 1 + 1 = 2 is pretty hard to disagree with as it is both very simple to understand and can be directly tested by a person holding up one finger, then another, clearly seeing there are two. We did this as young children and found the concept pretty easy to grasp. Pretty much every human agrees with this that does not have a mental impairment.

So I'll claim a thing is highly agreeable if:
1. It is very easy to understand
2. It is directly verifiable by anyone

Many things are not so simple though and cannot be easily tested by an individual. The concept of a thing may be very complex in itself and thus misunderstood what it is in the first place and even worse, contradict with basic intuition.

Let's take the extreme opposite of 1 + 1 = 2 and look at Evolution as a great example of a very complicated thing that many people disagree with.

Evolution claims that natural selection starting from microbes eventually gave rise to the complexity we see today in all species. This involves extremely long periods of time passing which humans cannot experience and the necessity of having to understand biology and other branches of science to a literate degree.

Evolution is both complex and not directly testable by an individual. Not only that, it requires a lot of work to try to build up enough knowledge to understand it in the first place and directly conflicts with many cultures in its premise, having alternate explanations that are closer to 1 + 1 = 2 in terms of the simplicity of the message.

So, then a thing is highly disagreeable when:
1. It is very difficult to understand
2. It is not directly verifiable by anyone
3. It contradicts with popularly held beliefs

The topics that most divide us are the complicated ones but unfortunately, the world is also complex. Humans will continue to disagree on things they cannot understand as easily as 1 + 1 = 2.

Possibly we will become more intelligent through technology and we will intuit physics at some point but we are a long way off from that right now.