> Hard to take him seriously when he doesn't himself pay more tax

Why? Advocating for a change doesn't imply that you need to act like that change has been made already.

For instance, I am a huge advocate for building out more sidewalks in my city. I don't currently walk everywhere, though, because the sidewalks today aren't suitable for that -- the change needs to be made first.

Likewise, I could donate all my spare money to the city to fund sidewalks, but this goes against my visceral sense of fairness: I am advocating for my local government to build sidewalks, not saying that sidewalks should be built by any means necessary and that I'm willing to foot the bill alone.