[zo1]

"If a large number of individuals or businesses are heavily invested in the-way-things-are, is it ever dangerous to rapidly change the market rules that we've built up- usually for the purposes of consumer protection or fostering businesses that benefit the larger community?"

Drastic and radical changes that happen quickly are probably quite a shock to a lot of business/industries/people. However, we must take care in what "regulation" or "consumer protection" as you call it, we add lest we actually make the subsequent change more drastic and actually harmful(more so than the harm we're trying to prevent by putting the regulation in place).

We're only in this situation because of regulation designed to protect already-invested businesses. At the time it was probably argued that having them fail would be a "dangerous and rapid change", or something to that effect. And the regulation sort of propped up or let the businesses get even more heavily invested into their ideas with no fear of alternative markets etc.

We could argue that if those regulations never got in place, those relatively smallish businesses would have failed at the time. The then owners would have adjusted, started over, or re-tooled their business to fit in.