You are not being kind you are belittling and making a real event that hurt many into a silly game. Racism and slavery are real things you and your co-workers can fight against them if you truly care.
Get in touch with the oldest org fighting slavery: https://www.antislavery.org
They could use your money, time and network. The one thing they don't care about is changing master to main in your github repos
Also you said "high rewards". What are rewards in this particular case?
However, there are groups of people at my work who say that “main” is a less controversial term and in fact a better term for a “trunk” of code development (“mainline”). Since I see no harm in using it, I figure, why not?
The rewards for me are having better relationships with my colleagues and less friction, which in turn leads to a more promising long-term career outlook.
I will admit that what makes this easier for me is that I think society is generally moving in the right direction, towards more diversity, more equity, more tolerance, less racism, etc. If I felt things were going in the wrong direction, I would stand up against it. But it's always easier when the river carries you in the direction you want to go.
Sorry I don't have a great answer here, but what I do know from experience is that most of the time, standing solely on principle while the hilltop is crumbling underneath you isn't a very safe place to be. :-)
You seem to be conflating controversial with clearer
We have no obligation to do or say anything other than "What you're telling me to do is unreasonable, you can get stuffed."
I've personally made the change because I see no harm in it, and it makes my colleagues happier. Being kind and considerate has low cost and high rewards.