I've thought about this recently.
Rather than being a forum about model engineering, it's a forum for model engineers in the broadest sense.
If a number of forum members are interested in a topic, then they should be free to discuss it (in the right topic).
What would be wrong is the unlikely situation that people who do not share our 'common interests' start using the forum as a convenient place to discuss their interests.
It's not the job of moderators to limit the topics of discussion (aside from those likely to spread disruption), but for forum members to vote topics up or down simply by deciding whether or not to participate in the threads.
We did, however, establish topics like 'Related Hobbies', 'Vehicle Restoration' and 'The Tea Room' for those of a particularly sensitive disposition.
Neil