Fact or misinformation?

I don't know about everyone else. I have thousands of records and maybe 30 mono ones mostly old Jazz. Spending Thousands of dollars to get a mono cartridge as good as the stereo one for 30 records seem a bit odd almost as bad as buying a reel to reel to play the 30 or so prerecorded tapes that exist.   

Dave is entirely correct. There is one instance that might damage a stereo cartridge and that is trying to play 78s with it. The groove size is much larger and a modern cartridge will bottom out in the groove encountering more friction than usual as the point digs into the shellac. 

I do not bother with mono cartridges. A stereo cartridge will play mono records just fine. Imaging is not important as there is no image. Mono records actually sound best off axis.