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.
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