Traffic accidents happen. According to your reasoning, we should forbid people from owning and driving a car.
A related question I want to ask is: what is inherent about software that makes it not okay to have restrictions on modifications where lives other than the owner's may be at stake? I see other comments here that say things like "oh these machines should have mechanical limiters etc. that prevent them from being dangerous." But isn't that essentially the same thing, just implemented in hardware and not software?
I'd like to note that I'm not saying that John Deere is in the right here. I just feel that the argument in the parent comment is, for lack of a better word, inhumane.