The only thing it can "prove" is that a person has the ability to memorize individual card meanings. And that's all their tests amount to. But reading isn't memorized card meanings. It's so much more.
Have a look at some of the U-Tube instructional videos or readings done by supposedly expert readers. What do you see? You see "this card means this" and "that card means that". You see individual card meanings, recited one by one. You don't see the reader weaving all the cards together or giving any kind of a cohesive, insightful, meaningful reading and certainly nothing psychic or intuitive. At least, the ones I've seen are that way. In order to achieve your goal with these schools, they require money---big deal, the money---and for you to do a few readings using memorized card meanings, and maybe for the higher "degrees" you might be required to do a bunch of writing and turn it in (and take a chance that anyone actually reads it) and maybe having taught a class or two with your memorized meanings---oh and once again, the money---plenty of money.
If I were to walk into a Tarot reader's booth and see the "accredited diploma" and a "code of ethics" there, my attenae would wiggle and I'd see the indications that the reading I'd get might not be a real, cohesive reading but rather a "this card means this" reading.
Don't get me wrong. Many people who shell out the money and post the certificates may go on to be dynamite readers in the long run, who can weave a reading together and glean the real insights to be had there. But a whole lot are going to believe that "this means this and that means that" is what a reading is supposed to be.
One of my concerns is that, after years of people going through these "accredited" schools, even the public is going to start believing that those simplified, memorized, single card meaning readings are the real thing and then where will the real reading tradition have gone?
Note: Codes of ethics are fine if you want to post them. I wouldn't post one because I figure my actions and my readings should speak for themselves but if it makes you feel better, go ahead, I guess. It would still just say "young'un" to me.
If you feel more professional putting up your code of ethics, more power to ya.
Coming back to add that this is just my opinion. If it's unpopular or you don't agree, that's okay, too.