What exactly are taxes?

They are the confiscation of a percentage of the fruits of labor of individuals by a small group of people who claim the moral authority of such action, and enforced through violence and coercion.

Claiming a percentage of the rightfully owned property of another is the same as claiming ownership of that person's life and rights.

And is thus a claim of slavery.

All taxes are immoral and illegitimate, being basically a claim of slavery.