There have already been otherwise intelligent, interesting and helpful members that are not here because of this, such as blueskull. I'm not advocating much stricter control or moderation, but making even a specific area 'wide open' is likely to significantly change the overall character of the forum.
OFFTOPIC
The case of him is different. We are talking about threats to people in the forum and Dave itself, as his brand and sponsors.
Plus he was tons of times warned regarding his stance when someone would talk about his home country. He could simply keep it quiet and silent, don't feed the noise but he always responded.
That's keyboard wars, you let them go if you want:

/OFFTOPIC
Regarding the issue in hand, from what I see in terms of offtopic (and I'm also one that sometimes fall in such) normally it tends to go to 3 or 4 posts and then tones down
Example -
https://www.eevblog.com/forum/vintage-computing/orcad-for-msdos/msg4403527/End of Page 3 to forward.
Am I OK with it? Yes because is not offensive, divisive or hostile. Mostly is fun "Watercooler talk" related with the subject in some way.
Now if it goes into political/religious/personal beliefs where people fell that it may affect them that's the problem, and then we go again to the top of this post.
That's keyboard wars, you let them go if you want.If someone wants to stop the offtopic just do what I see being done in some posts, just finish it by going again on topic.
Now an IDEA: Dave and the SMF administration, is there any way of creating a function like the quote?
Like a quote one that is always hidden until someone clicks over it to show the contents. That way people could offtopic inside a topic and the thread would be minimised by default until you clicked on it, kinda like how Reddit does with the negative karma posts.
It minimize them with an indication of how negative they are and you click to read on them by your own choice. That way the thread would be on topic and further offtopic derived from the thread subject itself contained hidden until clicked.