Question

I’ve seen many times in your writings that you support Kant’s position that the criterion for judging a moral act is whether the person doing it would think in his heart that he would want this to be the rule. (Forgive me, I’m expressing myself a bit clumsily.) That is, I won’t evade taxes even though my action has no effect whatsoever. Because it’s immoral! And who decided that it’s immoral? The very fact that I wouldn’t want everyone to act that way, or that if everyone acted that way it would lead to disaster, defines the act as immoral. Even though you repeatedly clarified that my own act, by itself, has zero effect, still it is not moral. Up to here, I hope I understood you correctly.
I don’t have Kant’s book, and in any case I probably wouldn’t understand what he is saying, so I’d be glad if you could explain to me why such an act is considered immoral. With theft, everyone feels that it’s immoral, but with an act that affects nothing, there’s a very strange feeling about it. I’ll make the effort and vote in the elections because what? Because I’d want everyone to vote? What’s the connection?
Forgive me in advance; I’m sure this has been asked before, but I didn’t find a clear explanation. Thank you very much.