"If the coral in the shop is collected as dead corals then there is little, if any harm done. It they were harvested live, major education of vendor and collector is in order (along with hefty fines). Unfortunately, there is no good way for authorities to know."
The collection of dead coral ("live rock") is actually quite destructive for a number of reasons. This is done not just to support the aquarium industry. One of the major uses of live rock is for building materials (houses, roads, etc) throughout the tropical pacific. Most of this isn't even for commercial use. But given the status of the human population, even subsistence use adds up to be devastating. Even on the reef flat where I did my dissertation, almost all the live rock was stripped in less than five short years. These used to be prime habitat and offer rare solid refuge in seagrass beds for blue rings and other pygmy octos. I'm always shocked when I go to a healthy reef flat that still has some left. It's a shockingly rare sight. When collecting the rock, and dead coral, the octos get collected and killed too. Often to make live rock, live coral s brought in close to the beach and the coral allowed to die there, before it's used. Basically because there's no naturally dead coral left, they have to kill the coral to make it. As the coral dies it stinks like crazy, so they'd rather it stink on the beach and get washed/sun-bleached in the intertidal a little before using it. It's not unusual to see piles of rock 2m in diameter and .5m high in this state. The scale at which this occurs, both collecting live and on rare occasions naturally dead coral for this, depletes shore-line protection and erosion control on tropical islands all over. This is why live rock is also protected from collection in the US.
Also- coral rock degrades extremely quickly in the wild after the animal dies; it is taken over by algae and the rough surfaces very quickly smoothed. Naturally dead coral could not be sold in the curio trade (as in the pic). You can be sure that- if you see coral for sale like this in a shop that it was prepared from live coral and killed (usually using a dilute bleach solution) to clean off the polyps.