If you had seen lots of resumes and references, then interacted with those people later, you'd distrust resumes and references too.

One can distrust without being so overt about it. If I get that vibe from a potential employer, I walk out. It shows that not only do they not trust me but they either a) also don't trust their own natural vetting ability/competency and/or b) are just assholes.

Why not at least give the appearance of trusting while still making internal judgements and while holding some sort of casual conversation about technical topics with the candidate?

Out of curiosity, could tech screenings via phone/skype have helped in avoiding that situation? (Or perhaps they have already not helped?)

Yeah, phone screens help a lot. But people can still sound convincing enough on the phone for half an hour without being a good programmer, so that's just another filter layer before an on-site interview.

I actually don't mind the day-of-interviews thing because I find it fair and encourages hiring efficiency. For example, if I lose a day to do 6 interviews then the company loses 6 engineer-hours (+ time to write and assess feedback). That will discourage doing a large number of interviews with a low hire rate.

OTOH, I hate having interview "homework" because they take a lot of my time but cost the company almost nothing - they can easily have a hundred people doing the homework, get one engineer to spend a day evaluating them, and then only hire one person.