I am a member of a society which has a representative government which acts on its behalf. I have used their services and therefore I owe them money. Therefore, it is legitimate for them to demand that money from me.
And both these entities can do so legally. It would be entirely legal for the mafia to use the legal system to demand money from you in the same way the government would (or that any business or organisation you used services from would). The very fact they choose not to, suggests their claim is illegitimate.