You're leaving out the fact that Dixon was 18 years of age: thus, and adult in the eyes of the law. Sex between a minor and an adult is illegal. Do you wish to change the law to make it okay? Your objection appears to indicate as much.
Should we just throw all male high school students in prison then? They're all felons under this ridiculous ruling.
If they are legal adults having sex with minors (statutory rape), then yes. Unless, of course, you want to encourage that sort of conduct.
But in the final analysis, you are not the father of the 15-year-old girl, so I don't think you have much room to pitch a fit in this case.
If this were a 40-year-old man then I'd say prison time was appropriate...but it's not. They're both in high school. Silly me.