It's an exercise in very obvious question begging. If the IRS collects taxes that you owe, that is "aggressive force"; if a landlord collects rent that you owe, that is "defensive force." Why? Because right-wing libertarians don't recognize the IRS's claim as legitimate but do recognize the landlord's claim as legitimate. Why? Because they oppose "aggressive force" but support "defensive force." If you tell them that that is circular reasoning, they respond with some variation of "I hate you."
The ideology has its roots in industrialist lobbying (
https://en.wikipedia.org/wiki/Foundation_for_Economic_Education) so there's no intellectual depth to it, but some people have a strong emotional connection to the powerful (we call them "authoritarians" generally, but they try to turn that meaning on its head).