It is impossible protect individual rights by violating them. Which means voluntary funding is a prerequisite to any honest security organization.
The thing that distinguishes a govt from any business or charity IS forced funding. There is no concern over whether "customers" are satisfied if you get their money whether you serve them or not. This is why a cop can shoot your dog with no need to worry about his job security.
The only thing that really keeps any organization honest is the threat that comes from the withdrawal of financial support. If an org is voluntarily funded, then the better they satisfy customers, the more money they make.
An organization funded by force creates an inverted morality where every employee of said organization can only advance their career by finding new ways to force more out of everyone around them.
And a force funded org will always grow. If people have no ability to refuse to pay, then they cannot prevent the growth. That growth will evenutally corrupt all other orgs by using money extracted by force (or printed at the expense of everyone) to support businesses & other orgs that most didn't want to support.
Govt which is by definition a financially unchecked organization, removes the natural market checks on all other orgs, & slowly corrupts everything, from the business of serving people, to the business of enslaving them.