Well, they do say opposites attract, right? That's about the only reason we can imagine why Jack's mom and dad got together, because Jack's father is his wife's polar opposite. For example:
It's true that some of his bad points might be explained by his time served in World War II. We learn in several places that he's seen some horrible things and has probably had to do some pretty bad things, too. But does going to war give you an excuse to be, well, a terrible person? Let's take a closer look.
Dads are supposed to be role models for their sons, right? Not in this case. Most of the time, Jack's dad is off chasing after his own pursuits, and they're pretty childish pursuits. Like the airplane he builds. Not only does he create an illegal runway for it, but he explains his wanderlust in pretty juvenile terms: "You and I are building a runway out back and we need that field so we can fly anywhere we want at any time" (4.62).
He doesn't really know where he's going or what he wants to do; he just knows he wants to get out of Norvelt. Did you ever try to run away when you were younger, and get like halfway down the street before thinking, "Gee…I have no clue what I'm doing?" That's Jack's dad.
That might be excusable for a kid, but for an adult—with a child and a wife—it just seems selfish. And Mr. Gantos's other actions aren't any better, like when he has Jack mow down his wife's cornfield, because he wants to build a runway and a bomb shelter. He makes this decision all on his own, without even discussing it with her first. So much for teamwork in the family, not to mention that she was growing the corn for Norvelt's poor people.
Now, all of this wouldn't be too terribly bad, but by the end of the book, Jack's father goes from being someone who is just kind of an immature jerk to someone that we (probably) actively dislike.
Jack's dad is basically a big kid, but there are a few moments where he seems to have some kind of adult-type insight. One is when he remarks that Mr. Spizz will eventually "flip his lid" and end up hurting someone (3.24). Guess what? That's just what he does.
Another is when he decides to not build the bomb shelter after all. This happens just before the end of the book, and occurs after Jack shows his bravery with the dead deer. (For more about Jack's maturation, check out his section in "Character Analysis.")
So, it's almost like Mr. Gantos is "growing up" at the same time his son is, and learning along the way to conquer his own fears (like the fear that the Russians are coming). Great, right? Better late than never.
Unfortunately, Jack's dad never quite makes it to adulthood.
At the very end of the book, Jack and his dad take a ride in Mr. Gantos's airplane. But it's not just an innocent jaunt. While in the air, they throw red-paint-filled balloons at the drive-in movie theatre screen. The moviegoers don't think it's too funny—shock! In fact, they all get kind of scared.
When Jack finally stands up to his dad to say that the prank isn't funny and that they're scaring people, Mr. Gantos doesn't care or act remorseful at all. His attitude is basically, "Whatevs" (check out 28.105). He sure hasn't learned anything from what Jack tried to teach him: "[I]f you do something bad and forget about it, then you might do the same bad thing again. But if you always remember it, then chances are you won't do the bad thing twice" (23.46).
This parental unit seems doomed to repeating the same mistakes over and over.
One of the main reasons Jack's dad hates Norvelt is because he believes it's a "Commie town" that focuses too much on communitarian values instead of Good Old American Capitalism. He thinks Florida is "where a hardworking man could make big money building houses for rich people" (4.51). In contrast, he views Norvelt as "a dirt-poor Commie town that is dying out" (4.41). He considers himself a "real man" (4.43), compared to all the "Commies" that live in the town.
Is this true? Without saying anything about whether he's right, we can point out that, well, we wouldn't believe much of anything that Mr. Gantos said. He's such an unsympathetic character that all of his ideas (and ideals) seem just a little suspect.
Not to mention that his hatred of communists seems just a little bit irrational. Sure, lots of people in the 1960s were worried about Russian communists. But Jack's dad goes a little further ... all the way into crazytown territory. He believes that the Russians "had already sneaked into the country and were planning to launch a surprise attack" (1.33).