Ultimately, a private forum is a benevolent dictatorship. If I had the skills, time and motivation to build a similar site, I would entertain suggestions from members and perhaps modify rules when there is consensus. I would not commit myself to a majority rules situation, though. Tyranny of the majority is as fearsome a situation as the tyranny of a ruthless autocrat.
For me, the problems seems to be more one of tone and politeness than of specific topics. Many problems in rural life and tractoring will be impacted by laws and regulations. By definition, these are political. Some of those political issues are local and non-partisan. Others are national and international and highly charged. If all political speech was removed from the site, it would be pretty bare of content. In general, I think when rules or laws try to be absolute, they fail. (exceptions exist).
I'm with those who would keep the forum as open to topics as is possible. First, give public warnings and then remove posts and/or threads and/or posters if unwanted content continues. Like most things, the market will decide.