Comment: Part of the reason you pay

Part of the reason you pay people is that the goal is not to just get people who are willing to donate their time, but to get people that are very talented. You want highly talented people in charge of the military, the deparments, the justice system, Congress, etc.

Another reason, which of course a goal that has failed miserably, was to prevent bribery. A policeman who is getting well-paid is more likely to not take a bribe, because he wants to keep his job; the risk of getting caught is too much. A policeman who is getting paid poorly (like they do in China and India) is more liable to look away if he gets paid well. If he loses his job, well, it was a bad job anyways.

Of course, there was a long period of American politics where people did freely give their time. A time when people who retired from politics did not immediately go join a corporation.