I often think about this. I don’t think it’s wrong to provide selfish reasons to do the right thing.

In the end, the world is full of people with different priorities and ways of thinking, if you restrict yourself to only the “pure” morality arguments it’s not like you can use the purity of your argument to correct the brains of all the people who are not swayed. But if you provide a variety of arguments you’ll convince lots more people.

And in reality most people are not pure selfish or pure selfless. Spoonful of sugar (selfish benefit) helps the medicine (selfless morals) go down.

Not trying to entirely quench your cynicism, just lightly cool it.