In what way is forcefully taking money ethical?

Forcefully taking money (i.e. taxation) via an entity that can imprison and economically suppress is not only wrong but it's responsible for atrocious assaults on human rights. Involuntary funding is the greatest threat to free speech and dissent. Involuntary funding is the greatest contributing factor to increasing wars of aggression, corporatocracy, war profiteering, loss of human rights, growth of a surveillance society and unaccountable budgeting, funding of special interests, and the overall escalation of the fray of mass merchants of death and greed wearing tailored suits. These are the people who appeal to simpletons that taxation is patriotic. Patriotism is nationalism. Nationalism is ignorant and complicit to atrocity and unethical behavior. It's a tale as old as history. That's what happens when people can't abstain: centralized power turns into an oppressive, uncontrolled, unaccountable force.

On a moral basis, avoiding contributing to the funding of behavior that one morally objects to is actually an act of great ethical and civil disobedience. One's life, physical freedom, reputation, and economic mobility are all at stake with such dissent.

How is this moral objection unethical?

The answer is that it's not "unethical." Conversely, forcefully funding any entity of institutionalized oppression is unethical.