Fact or misinformation?

@intactaudio +1

No...in fact a mono record can sound quite good played with a stereo cartridge. Especially if you engage the mono switch on preamp if equipped. You can buy an in line mono/stereo switch. I opted to go the mono cartridge route, Grado, as I have a removable headshell for easy cartridge swaps. Keep in mind though, mono cartridges/stylus should only be used on older true mono records....the later "dubbed" mono records can be played with stereo cartridges as the grooves were cut in the same manner as their counterpart stereo versions. The grooves on the older mono records were cut differently with wider grooves. 

I haven’t had a mono cartridge since the early seventies and have never had an issue.

All the best.

The big difference between a mono cartridge and a stereo cartridge comes down to noise pickup.  A true mono cartridge has the coils oriented to only pickup info in the lateral direction whereas a stereo cartridge is oriented with the coils at 45° to pick up info in both the lateral and vertical direction.  If converted to mono at the cartridge, the phasing of the stereo coils is such that the lateral info sums and the vertical info is nulled.  this null only becomes perfect if the info in the vertical direction is identical in both channels which never happens in the real world.  If the summation to mono is done by a mono switch this noise cancellation is less. The net result of this is since a mono record has only noise and zero musical content in the vertical direction,  a true mono cartridge can be much quieter in the groove than a summed stereo cartridge.

at the end of the day a cartridge is a compliant lever with a needle and either one or two electro-magnetic coils at the other end (or magnet moving inside a coil).

Mono records only have a single direction of displacement.  Stereo have two.

But either way its a compliant diamond sliding through wiggles. A stereo needle will simply pick up the exact same movement on both channels.

I do not see how this will damage anything.

I admit i've never looked closely at how they align the squiggles

So i find this assertion very unlikely