I also want him to have grades that will make him a realistic candidate for graduate school if he wants to go. I don't want to waste my money. Not on your life. Well, of course, it's not. But your parents expect more, and you should, too.
College is a lot about books and grades.
Grades are the scorecard by which you will be judged. And, like it or not, even the brightest high school students sometimes don't do as well in the college classroom as they or their parents expect. College is harder. Certainly, grades aren't all that matters, but it is an indication of your accomplishments. Your expectations for parental financial support during your college years can continue to be a source of conflict.