Ma Ying Jeou and the KMT have some persuasive arguments; there was an interview on YouTube where he eloquently explained why these claims exist; the mainland Chinese Communist party came to power without being elected by the people. Also, when Japan signed its surrender papers giving up its claims to annexed territories, the sovereignty reverted to the KMT government.
I mean, the KMT of that era would have had even less of a claim of being the legitimate representatives of the people for any reasonable definition of "the people".
