No, there are some very significant differences. First, there isn't any reason there would only be one ratings organization, one insurance company, and one Yelp-for-doctors. You would be able to reject or accept the rating of any person or organization, and so would everyone else.
Second (but related to the first difference), the main problem with a title of nobility is that it grants legal privileges, thereby erecting legal barriers for others. That doesn't happen in this scenario.
> First, there isn't any reason there would only be one
> ratings organization, one insurance company, and one Yelp
> for-doctors. You would be able to reject or accept the
> rating of any person or organization, and so would
> everyone else.
This is true--at least at first. I suspect that whatever ratings mechanisms develop to fill the void, they would eventually coalesce into a single entity (or maybe a couple of entities with geographic specialties) that would, with time, come to enjoy de facto government sanction. This is one instance where I think most people don't actually want variety and choice. 100+ ratings organizations are useless if none of them have any data on the doctor in question (to continue with the physician example). So whichever ratings systems get an early lead would quickly dominate. And once they have achieved monopoly status they can shut out anyone who doesn't want to play ball with them. The general public can of course ignore these ratings, but they would do so at their own peril. (It's worth noting that you can already ignore the "ratings" of physicians and go see unlicensed doctors right now).
Now, as for your point about eliminating the legal barriers to practice-- ie anyone can practice medicine-- while removing licensing would eliminate direct legal action (ie no going to jail for practicing medicine without a license) I think it would instead lead to increased civil suits. Consider: right now if a licensed physician is prone to malpractice or has other deficiencies they are forbidden from practicing. This can happen without anyone being actually harmed. On the other hand, if a physician gets bad ratings from yelp-for-doctors then they just need to find uninformed consumers or at least people who chose to disregard those ratings. When members of the public are inevitably harmed by poor doctoring they will have no legal recourse but to sue the doctor. True, they could avoid going to that particular doctor again, but the damage is already done. I'm not sure if we actually want more lawsuits to be brought against professionals-- it may end up making the cost of their services even more expensive than they are now, wiping out any cost savings from them not having to go to school and become licensed.
I guess my point is that there is no free lunch: guilds and professional societies are ancient institutions and they enjoy legal status in recognition for the useful role that they have in serving society. It may be fun to speculate what would happen if they vanished but don't be surprised if the institutions that arise to replace them necessarily gain the properties of the original institutions.
"I suspect that whatever ratings mechanisms develop to fill the void, they would eventually coalesce into a single entity"
I know you're speculating, but I don't think that's realistic. For that to happen, people would have to unanimously agree on a single rating mechanism.
As for doctors, their guild gives us a great example of what actually happens when guilds enjoy special legal status. Guilds and professional societies work to restrict entry into their fields, in order to prop up their own salaries. When they do this, they usually claim they are simply ensuring high quality.
Second (but related to the first difference), the main problem with a title of nobility is that it grants legal privileges, thereby erecting legal barriers for others. That doesn't happen in this scenario.