How do you defend yourself from an accusation 40 years ago.
I agree with this sentiment, but there are some corroborating details which side with the accuser.
1) She doesn't have too much to gain by making something like this up. She's a well-respected academic, with a stable career and presumably the reasonably stable financial situation that goes along with that. She's going to be pilloried, have her home address listed on right-wing sites, and more or less have her character and reputation questioned from every conceivable angle. And it might not even stop Kavanaugh's appointment.
2) She produced notes from a therapy session that occurred years ago where she described the attack by someone who was currently a high-profile federal judge. This creates a TON of credibility that at least SOMEBODY high-profile attacked her once upon a time. It doesn't name him specifically, but it would be pretty odd if it was someone else, and she just went after Kavanaugh for political reasons. See point 1.
3) She names a witness, which is a needless complication if she were making it up. She could easily say, "He pulled me into a room alone" which would be a lot harder to verify/deny. The witness is somebody that Kavanaugh actually knew, which suggests a case of her fingering the wrong person is very unlikely.
4) That witness has previously published a book about how drunk he used to get at parties all the time when he was in high school. There is a character in his book named "Bart O'Kavanaugh" that evidently gets drunk at parties a lot and pukes in somebodies car on one occasion. This lends credibility to the idea that Kavanaugh might very well have been an excessive drinker in high school, and she describes encountering him when he was obviously intoxicated.
Nothing concrete, but a metric ton of circumstantial evidence. I think it would actually be quite remarkable if her story turned out to be false. It might not be enough to convict without the testimony of the friend, but we aren't judging whether he should go to prison or not. We are judging whether he should get a seat on the Supreme Court. I say no.