I too have a reef tank, and I can attest that some corals are very resilient. I don't touch any while diving, just because I would rather be safe than kill something accidentally. To propagate corals usually involves cutting and touching and rubber-bands to attach to rocks. Of course teaching an entire community which ones to avoid is not possible, so they teach to not touch anything, which is fine. Besides, most live corals probably will not be sufficient to keep you in place. Just like gloves and knives, they can be used safely, of course you always have a few bad apples...
Also, holding your breath is another thing that we teach the extreme on. It is not holding your breath for a few seconds while you snap a shot that is dangerous. It is holding on ascent, or enough to cause C02 buildup.