By "dirt" you mean "something that would clearly make him unfit for the job".
No. I mean anything that they can use for political advantage. Something that proved he was unfit would qualify, but that's certainly not a requirement.
If there's nothing like that in those files, then there's no reason not to release them all and to allow everybody the time to read them thoroughly, correct?
No, that's not correct. There are a number of other reasons for Republicans to want to hide those files, including setting a precedent for other Trump nominees, preventing the release of stuff that would embarrass somebody
else, and preventing the release of something that might make Kavanaugh look bad but shouldn't actually be disqualifying.
Note that I'm not arguing that any such motives actually justify not releasing the files, but there are clearly other possibilities in play here.
It's certainly true that some people deem him unfit for the job based on what of his past record has already been released.
Some people? Try basically every Democrat senator.
This, of course, doesn't imply that none of the people speaking out about this situation don't also care about transparency in these proceedings
The senate doesn't care about transparency except to the extent that they can get political advantage from it. That cuts across party lines. I'm sure some of the people outside the senate calling for the release of the papers genuinely care about transparency, but this is hardly the first or the last example of a lack of transparency in government. It's fairly unremarkable in that respect. I'd like more transparency in general, but the reality is I'm unlikely to get it.
or about the fact that if it goes through then a man who is under criminal investigation has been able to choose his own judge.
Yeah, not really. If the investigation turns up anything real and significant about Trump himself, the relevant legal remedy will be impeachment. In that event, the Chief Justice would preside over the trial in the senate, and that wouldn't be Kavanaugh or any other Trump-appointed judge. The Supreme Court would have no other role in impeachment proceedings, and even that role is pretty limited.