Imprisoning someone for refusing to pay a $5 voluntary debt is morally different from imprisoning someone for refusing to pay a $5 involuntary debt. It's important to understand that all government mandates are backed, ultimately, by the threat of violence/imprisonment, to inform our decisions about what behaviour to mandate.
While that's true, it's important to keep a measured understanding that it's a rare occurrence and the threat is only there because we haven't figured out a way to enforce rules without it. There's a big difference between something where prison happens 80% of the time and .01% of the time.
The carrying out of the threat may be rare, but the use of the threat to deprive someone of their rights is not. It is endemic. A person has a right to their property and their privacy and income tax laws violate both.
