Either one of two solutions needs to be adopted:
1) clear rules involving off topic comments need to be established and enforced on all forums all of the time,
or
2) the OT rules need to be ignored and only personal attacks or hate speech needs to be restricted.
So far, most voters seem to prefer some happy medium between rigid adherence to topic and total free-for-all. So if the preference is for something in between, what might such rules entail? "Off topic comments are allowed/prohibited unless ..." what? I'd like to hear any suggestions anyone might have.
However, I'll have to say that IMO the goal of their being established and enforced on all forums all of the time is a pretty high bar, considering the forums are moderated by different people, who do the job as part-time volunteers and aren't always online, and probably would each have their own individual interpretations of the rules.
As someone who occasionally posts OT comments myself, I'm not averse to some OT discussion. My biggest objection is when an OT conversation is interesting enough to deserve its own thread. If it's kept in the original thread, people who might like to comment on the subject, but who aren't following the original thread, won't find it.
Otherwise, OT posts bother me only when they're SO unconnected to the topic at hand, or even the forum they're in, but draw enough other comments or counterargument as to distract people from the subject under discussion, that the original conversation gets completely derailed.
But moderating to eliminate these would require case-by-case judgment calls.