Geez, next to vinyl vs. the "D" word and Tubes vs. SS, the Mag vs. De-mag topic seems to split audiophiles like few others. You hear all kinds of comments pro and con. To make matters even more confusing, I've heard cogent, convincing arguments from both sides of the issue from people whose opinions I respect highly.
I've never tried de-magging any of mine for fear of the a) on Marakanetz' list above. With my budget, I can't afford to ruin anything. Like Doug, I've tried the Cardas sweep record and found that there was no difference after using same. Now, I am not sure if it is because my cartridge was not yet at a stage where it needed treatment, there were other issues at play, or if it is just an ineffective product for my cartridge. But, it seems to have worked for Doug and he has a good ear for his system.
Some highly esteemed members here swear by the demagnetizers like the Aesthetix Benz, etc. while others swear they can ruin the cartridge or will cause you to require more and more frequent use. Kinda like the older rechargeable batteries.
Color me confused.