Debating Bitcoin with my Father in Law

My girlfriends dad is insistent that by Bitcoin being infinitely divisible, it's no different than how they print more and more dollars. He reckons and says "what happens when Bitcoin becomes so expensive that people can't afford to buy or use it and I was wondering if that's a real possibility or not. I'd like some people to weigh in and maybe help me explain or articulate better that it's the opposite of inflation. He also is insistent that it has no use because it's not backed by anything. I tell him it's the utility behind it that gives it it's value and then he says at some point it has to collapse because it's not "real"...

Edit: Please keep comments respectful! There's no tension, I'm just genuinely looking for an explanation! He's a cool guy and he's playing devils advocate not necessarily being hostile! Also he'd like to know what would happen if the dollar crashes. Would BTC become worthless?