Hi Harma,
You're talking about bentonite, which is a very fine textured clay, traditionally used in foundries for making molds, (or moulds), into which molten metal is poured, resulting in a metal casting, after the metal has cooled, and the clay mold is broken away. Most of the bentonite that I've seen and used typically has a slightly greenish-gray color.
Bentonite's main attribute is it's ability to hold fine detail, (which is why it is used for mold-making), but it is also an absorbent, and it may have certain chemical properties. For example, in the livestock industry, bentonite can be used, (at levels of roughly 2 to 3 % of the ration, by weight), to mask the effects of aflatoxin in corn. IOW, aflatoxin is toxic to swine, at levels above about 100-200 ppb, (parts per billion), and at significantly higher levels, it will cause aflalatoxicosis, and liver damage. Adding 2 to 3 % bentonite clay to the feed ration, however, will completely mask the effects of aflatoxin, so that the swine are completely unaffected, even at relatively high aflatoxin levels in the feed.
So, if the cause of someone's MC is a toxin in the fecal stream, then bentonite might possibly render that toxin unavailable. For most of us, though, I doubt that it will help, because there's nothing magic about it, otherwise. It's just a form of dirt.
Eating bentonite is part of a treatment that has been promoted for years as "The Makers Diet", by Jordan Rubin, and he has presumably made millions over the years, from people who have fallen for his pitch. He sells all sorts of "magical" supplements that will cure anything from hangnail to heart attack.

He has a lot of "believers" who praise him to high heaven, of course. As the old saying goes, (which was incorrectly attributed to P. T. Barnum), "There's a sucker born every minute". What P. T. Barnum actually said, according to historical records, was "There's a customer born every minute".
http://www.quackwatch.com/11Ind/rubin.html
The poster you mentioned is correct - eating bentonite clay will not harm you, (it's not likely to help you either, but it shouldn't cause any harm), so eat away, if you're inclined to eat dirt. Personally, I stopped eating dirt after I was a few years old, after it apparently caused me to develop worms. I don't know how old I was at the time, but I can still remember how huge one of those worms was, (at least it looked huge to a little kid - that sucker looked as big as a full-grown earthworm), after I passed it, (after taking a vermifuge to kill them). Yeah, I spent a heck of a lot of time playing in the dirt, when I was young, but it apparently didn't prevent me from having allergy problems.
Tex