ISU was only better than Iowa during parts of the 70's.
I bet your old man came of age as a fan during the Evaschevski years, right? The Hawks hit heights in the late 50's/early 60's that ISU never hit. Kudos to your old man for sticking out the bad years (which true fans do), but my guess is when he was young and impressionable, had ISU been playing in Rose Bowls, and Iowa not playing in any bowl, he probably wouldn't be a Hawk fan, along with many of his generation. It doesn't make them dbags or anything, it's just the reality of the situation.
For me, even from a young age, the idea of cheering for your school just made sense. My mom was an Iowa fan because she went to Iowa, and my dad was an ISU fan because he went to ISU. I cheered hard for both growing up, pulling for ISU when they played. I was always drawn more to Iowa State as a college and community, and that's why I went here. A couple weeks in at ISU, and I just felt no connection or reason to care about U of I athletics anymore, as I had no connection to the U of I, where ISU was my life, literally. I was part of that community, and that included the football team. I couldn't bring myself to even half heartedly support the arch-rival, and I couldn't (and still can't) wrap my head around folks who openly put down their own college in favor of the arch rival.
They aren't putting down their college by rooting for a different team. The athletics have little to do with the university. They can be more than proud of their education. That's not going to change just because they root for Iowa in football. There is a tremendous difference between putting down your university (this school sucks, I should have gone to Iowa) and rooting for the Hawks while being proud of the education that ISU gave you.