That is really sad. I have only had one trespasser in 10 years of farm ownership in MN. What is the deal, why do people not respect property rights in Iowa? Are the punishments to lenient? The December gun season structure? What makes it so bad in Iowa?
I think our yesteryear deer hunting culture, particularly during the "let's get the gang together and round up some venison" early December slug seasons, still "remembers" a time when it was fairly common for big groups of slug gun hunters to literally line up and push across big stretches of ground with little regard to individual landowners along the way.
There were enough permissive landowners that the groups had a place to set up and go through that even if there were a few non-permissive landowners along the way it really did not influence them much. Realistically, it's not everyone that is going to confront a large, well armed group that may even have a bit of a reputation, etc... So there is some history of that style of deer hunting that people still base off of in some cases.
I hunted in South Texas once several years ago and the understanding there was that you didn't even
THINK about crossing a fence over to ground you didn't have permission on. For a variety of reasons, but I would sum it up and call it culture, trespassing was not at all common or tolerated.
Perceived penalties, or a lack of them, whether in the form of hefty fines or risk of getting confronted by someone else, etc, influence the psyche of potential trespassers. I suspect South Texas has been "tough" on trespassing for a number of years now relative to how things have generally been in our state. Generally speaking, Iowa has not been too tough on trespassers in the past. Deer hunting has been more of a social thing in many cases and many landowners did not care OR enforce their property rights that aggressively.
Nowadays that is changing more and more though as people that either own, or control via leasing, ground that they "care" about what happens to the deer herd are influencing things more.