I can't imagine that normally closing a gun (neither slamming it closed or gently babying it) and allowing the bolting springs that the manufacturer designed would harm anything. That certainly would not even approach the dynamic forces that occur upon firing. Babying the top lever closed could leave the bolting surfaces not fully engaged. That miniscule amount of movement upon firing will start the process of the gun slowly beating itself loose. Forcing the top lever closed will be bad if that force exceeds what the maker intended in normal closure. Keeping the bolting surfaces and hinge surfaces clean and lubed and fully engaged, and firing ammunition that does not exceed design limits will insure long life. Good designs that self compensate for wear like Smith or Fox rotary bolting, or limit the forces of firing as found in Model 21's reduce the chances of going off face. Of course, some cheaper guns start life with sloppy tolerances and poor hardening of hinge and bolting surfaces, so they have a running start at quickly shooting loose. There was a good chapter on this in "Shotgun Technicana" by McIntosh and Trevallion.
