What makes him a rapist is raping somebody. What officially establishes that fact is a courtroom trial, which Trump had.
Nor need it be proven beyond reasonable doubt in a civil trial. Preponderance of evidence is the standard.
And Trump chose a bench trial (no jury), wherein the judge found the allegation of rape credible by that standard. That's all the due process that was necessary to grant a judgment on the plaintiff's behalf.
Would it matter to you to know for a fact that he raped somebody if he did? I don't think so. If not, why fight the allegation? Trump is clearly morally unfit for everything, but apparently not everybody cares about that. In fact, it seems like about half of Americans don't. And if that's the case, why pretend to care about such things?