If there is actually a debate, why not win the debate? That should defuse the hostile political environment. No?
Maybe you don't actually mean "debate the legitimacy"? Maybe you mean "assert, while blinding themselves to any alternative viewpoint, the illegitimacy..."
One who rejoices when everything is made as simple as possible, but no simpler. Sayer of things that may be wrong, but not so bad that they're not even wrong.