I wanted to punch Mr. Davis

I'd say that his tirade was partially justified as it was a mix of his emotions and Alice's past reputation working against her: he did list several things that Alice has done in the past then tried denying, only to be caught and proven that she was indeed responsible. So in his eyes, Alice was a habitual liar and he no longer trusted a word she said. They even showed at the beginning of the movie that he wasn't too fond of Alice and Darlene's friendship and was probably kind of happy that Darlene was going away to college and would not be seeing nearly as much of Alice as she was in the past. I think he always felt that Alice's family was beneath his own and Darlene was way too good to be around Alice.

The irony here is that this time Alice was indeed not responsible. IMO, that's why she yelled "I didn't do it!" in such an angry fashion in response to Mr. Davis' tirade. This just goes to show that one shouldn't be judging other(s) without knowing all the facts.

And yes, it would be interesting to know if he had a change of heart about Alice after what happened at the end; but I would not hold my breath. He probably thinks that Alice did it and should have owned up the second they were caught, took the blame upon herself so that Darlene was set free from the get go. What is obvious though is that Darlene will indeed do everything in her power to try to get Alice set free, I just hope her father doesn't get in her way of doing so.

P.S. I think a huge part of Alice's decision to take full responsibility upon herself was because she felt that it was her behavior that landed them into the mess they were in. First, she regrets not telling Darlene about her run-in with "Nick" at the market and him hitting on Alice right after Darlene's romantic night with him. Had she told Darlene right away, the whole Nick story would be over right then and there. Then Alice goes on: "What if we went to Hawaii like originally planned? What if I let you pay for those drinks by the pool? We would have never met Nick, we would not be going to Hong Kong and we would not be here." Alice felt that although she never smuggled drugs that she was accused of, she did set off the chain of events that got them to where they were.