Without police powers you will have a lot of people evading / not paying the taxes. Is your idea that the government set the taxes to a level where it can get by from those that pay? If it’s voluntary why not just have a system where the government has to convince people to donate what it says it needs and set aside the complexity and economic distortions and likely corruption of all the various taxes on different things? 

 You’re confused, we don’t have police powers today, hence why everything is so shitty and unsafe.  What you meant to say is that without stealing our police powers and then money, they couldn’t pay a special class of citizen to oppress us.  You see, as soon as everyone’s not equal under the law, someone, is someone else’s slave.