I left this comment on a popular Reddit thread, but thought folks here might also find it relatable.
The first time I flew first class (which was due to the kindness of another technologist who wanted to help me land a job by flying me to DEFCON), the way the other passengers treated the flight attendants disgusted me so much that I felt guilty sharing space with them. I tried to be kind and respectful in spite of the jerks, but it never sat right with me.
A few months later, another friend pointed out to me, if I hadn't been there, they would have had to deal with yet another rude, dehumanizing customer. It helps a bit.
"It costs nothing to be kind" misses the point, I think.
"Being unkind makes everyone poorer" is closer to the truth.