It required drilling down into these articles several layers (about 12) to find the relevant information.
First, the issue they complain about above only applies if the repair is with the computer itself. If the issue is mechanical, you're more than welcome to fix it, or have someone else fix it.
John Deere is claiming that to "hack" the software locks would allow people to reverse engineer their proprietary software, which has been held to be true for other digital software, such as online games and tax software.
This is very similar to the fight over "Right to Repair" for motor vehicles, which would force car manufacturers to release all of the same information to anyone who wants to purchase it, as they do to their own, licensed service facilities. (This is a state issue, so that is broadly generalized as what the proposed laws actually require is different between states.)
Slash Dot and Wired seem to be all over this, but their coverage appears to me, at least, to be a tad alarmist.
But a big California farmers’ lobbying group just blithely signed away farmers’ right to access or modify the source code of any farm equipment software.
In 2018 California has proposed legislation for Right to Repair and a lobbyist group agreed to the following exemptions:
It is worth noting, for full disclosure, that the Clean Air Act actually requires electronic emissions monitoring and diagnostics for motor vehicles, so for cars, motorcycles, and buses at least, the option of just going to a car manufacturer that doesn't make onboard computers doesn't exist in the US.