SCA aside...
If the king and queen aren't willing to vouch, either there's lack of evidence for them to believe that they can win an appeal, or they lack the ethical fortitude to stand up for their own people.
However, as a political entity, the SCA has the right to accept, deny, or remove anyone it so chooses, with or without reason. Membership, even paid, is not a right, so it would certainly be an uphill battle to wage... and if they win, at what cost? Ostracized by other people anyway? Thousands in legal fees? Hundreds of hours to push an appeal?
Politics is a fantastic way to rip any organization apart.