I suggest that all 'invasive posts' i.e. posts which have nothing to do with the subject of the thread be deleted automatically.
Too many times I have seen people post into threads which they have made no contribution to in any other way, just to spread their crusade, or to claim a centenarian thread.
Fair enough I have seen posts that were accidentally posted in the wrong place, but those are the exception rather than the rule.
Giok