I think there are two issues here.
I do not believe that, taken in itself - or even with Ramirez and Swetnick's claims -- Ford's allegations should have been enough to derail the nomination. This is not because I think she was lying; I believe something that could be classified as sexual assault happened to her, that Kavanaugh was involved, and that she is being truthful as she remembers the incident. However, memory is a tricky thing, and in a case like this, details make a big difference. If Kavanaugh behaved precisely as Ford describes - in other words, if he attempted to rape her -- that is disqualifying, no matter how long ago it was. If he rather did something that would be closer to groping, that's still bad, and still, a form of assault, but is not, in my opinion, something that means he is unqualified to service as a SC Justice 35 years later.
So, which was it? I don't know - and I don't think it is wildly implausible that, over the years, a person's memory could magnify what was already an upsetting incident into something even worse. There seems to me a difference, too, between not going to the police -- very, very common, and not something that says anything about Ford's credibility -- and not telling anyone that anything had happened for a full thirty years. Again, I'm not saying Ford is lying, but I tend to think the average fifteen year old who had experienced a violent assault that had stopped short of rape would have been visibly upset right after the fact, or mentioned something to a close friend, if not right away than a lot sooner than thirty years later. Which leaves me wondering if this isn't something that may not have loomed quite as large to Ford until it came out in therapy, possibly as part of the context of a larger conversation, and in a climate in which sexual assault was taken a lot more seriously than it was in 1982. Not a "recovered memory," precisely, but something bad that became something worse in retrospect, without any conscious attempt at deception.
Ramirez and Swetnick are less credible; I don't think Ramirez is lying either, but she admits to not having been positive that it was Kavanaugh before thinking about it for some time, which makes her claim very shaky. Swetnick isn't really making a specific charge at all; she's describing a culture, and saying Kavanaugh took part, but it frankly sounds like a sensationalistic extrapolation from her knowledge of the party scene.
However, all this being said: what I think is disqualifying are the transparent lies Kavanaugh told under oath. Whether or not you agree with every aspect of the article posted earlier in the thread, Kavanaugh's depiction of himself as a teenager was wildly disingenuous under any reasonable standard, and many of his attempts to discredit Ford were manipulative and logically suspect. It defies credulity to believe that "ralph club president" refers to vomiting after eating spicy foods. It defies credulity to believe that "Renate alumus" meant "I really respect this woman who I went on a couple of dates with." Multiple people have indicated that Kavanaugh was a heavy drinker, not just a guy who liked beer.
More than that, it is deceptive for Kavanaugh to claim that he couldn't have been at this party because he was away for weekends, as there is no reason that the party had to be on a weekend. Having a summer job does not mean you couldn't possibly have been drinking beers with some friends on a Thursday night. Even worse, Kavanaugh uses his calendar to "prove" that no such party occurred - but ignores the fact that the July 1st entry does include a reference to drinking beers with a few friends, including two of the people Ford places at the party. That goes beyond defend yourself; that's gaslighting.
I understand that Kavanaugh was in a tough position, as once you admit to being drunk enough that your own memories may not be reliable, it is very hard to then say "but I still think Ford is exaggerating," even though that may well be the case. But the fact remains, he was untruthful, and that, to me, means he shouldn't be on the SC.