Humans are shitty and historically when resources are scarce, those with power and the ability to persuade masses will find a scapegoat to blame their problems on to divert attention away from their own mismanagement, bad policy, or the economic or social systems they've constructed.

This happens with race, sex, religion, ethnicities, etc. all the time.

Country is failing? Blame the Jews, blame the Blacks, blame the immigrant (insert race or ethnicity here).

Unemployment is high? Blame the immigrants.

Race is a social construct though and what constitutes a race and who qualifies as a part of any said race has changed over time, which only further proves the notion is bullshit.

Racism isn't just a scapegoating tool to avoid blame used by the powerful and elites, but it's also a tool used to prevent mass movements that could change the status quo, keep people occupied over racial conflict so they don't work together to mobilize as workers against the bosses and executives who keep them in low wage, unsafe working conditions.

Racism is also a tool of colonizers and ethnocentric nations that they use to excuse or justify their subjugation of other people and the theft of their resources. "Old World" people labeling natives as savages and heathens (technically true that they weren't Christian but that's to be expected since they'd never have heard of Jesus) and because of this they "shouldn't be allowed to hold such troves of silver and gold or manage such fertile grounds when it could go to the glory of God and Spain! (or insert colonizing nation here) instead we smart, righteous, Christians should convert them and take their shit!"

So racism exists for a lot of reasons but none of them are good ones.

I agree, we should see each other as simply human beings, no one asked to be here, but here we all have found ourselves, let's do our best to make our stay here pleasant, and leave it better than we found it for those coming after us who didn't have a choice in their existing either.