I wish everyone is the same race.

Eventually, everyone will be the same race. 

Boiling conflict down to race is both woefully ignorant and asinine. The people constantly bringing race into the conversation here in the West are the ones who profit off of the division by hosting seminars to tell gullible progressives that they have generational guilt, a concept that would cause the entire world to implode if universally accepted. Thinking that if everyone had the same skin color that there wouldn't be division is the mentality of a 5 year old. If everyone were grey blobs we would still find ways to other different groups. Tribalism is inherent to the human condition. Fairly Oddparents had an episode on this exact topic. 

Social class discrimination exists very strongly even in countries with one race. 

We are all of the same race: the human race :)

If there´d be no more races, there´d be no more cultures, no nothing. And that´d be so fucking stupid I don´t even have words to describe it. Besides, we´d be killing each other over different things then, like ear shapes, or our opinions on pineapple on pizza (it absolutely belongs there btw). Hate is just a part of human nature and the sooner you understand that this is perfectly fine, the sooner your life will become much better.

Even animals have different variations, look at the huge variety of fur, feathers, beaks, .. - living creatures adapt to their local environment. It is normal and will always be there. Maybe in a few million years in the future we as humans will look different based on our environment. This could be life on a different planet (i.e. Mars) or our bodies might adapt to new challenges that may threaten our existence (to give us an advantage in creating offspring and surviving). When a person has darker skin it just means their ancestors needed this adaptation in order to survive as humans in their location (i.e. while they are not immune to skin cancer, the occurrence is less common. Similar reason why some people develop freckles after UV exposure). Certain phenotypes may also indicate biological health, or resistance to medical threats to our species.
If, however, humans looked too similar in the past, they avoided mating with them to avoid incest/inbreeding, and medical problems (i.e. their sons were sent away to another village or region in order to avoid that).

I also think that hate is a strong word - I don't believe that people truly hate each other just based on their race. There is more to it.
It is about elements of culture, legacy, the future and their own set of beliefs. In former times, humans used to associate (more) with others who looked like them as a form of protection against other tribes and this may increase trust in each other. When you meet people in business, your social life, through hobbies, (..) - you (often rightfully) assume that people who look, speak, or act in similar ways to us have common elements we can identify with. This doesn't have to be race alone and it doesn't necessarily mean that these groups hate everyone else.

Good example here would be how we form friendships and trust networks - a young, single man might have an easier time connecting with other young, single men due to shared interests, hobbies, sports, ..

That would just result in another distinction being made to create in and out-groups. Look at the treatment of different white groups over time in the U.S., thinking the bad treatment Italians or even Irish people whose home country is literally right next to the one who colonized America and whose people look really similar to the English. Some other grouping would emerge

You are a moron, humans will always divide over something. Race is just one of many things we divide on today