Revenue departments have many, many more sweeping powers...

Revenue departments have many, many more sweeping powers than any other agency or private collections firm would have under fair debt collection laws. So now what you'll have is revenue agents who are used to using those broad powers going after people who owe court fines or student loans. Some people might think this is great, but if you start unleashing the power of the government on those people, they might actually begin to chafe at such practices. I don't think it's a good idea.