I have listened and refrained from commenting, but I think it is time!

First, I am not the least bit worried about the weekend warriors and Soccer mom's taking my business from me. I do their children on a regular basis and many of them have equipment as good as mine or better. What makes them bring their kids to a professional photographer, when they have 5K worth of nice equipment?
Pretty simple, I can do what they can't, in a short period of time, without too much hassle and I give them a fantastic product they walk out of my studio with and go straight home and hang on the wall.
I spend 85% (if not more) of my time in Photography. (Not a day job.) I study child psychology, to be prepared for children, and to get the best photos possible without doing what mom does...run around snapping away with an expensive camera. I continually attend seminars and classes to keep me abreast of the latest in technology and technique in my industry. I attend professional guild meetings and hear techniques that help me bo a better, more efficient job, yet provides the product(s) a client wants. If a client percives that you are doing nothing more than what they are doing with the same camera, you are toast. Why would someone be willing to pay you to take photos? There must be a reason for them to come in your studio.
So the difference between part-time and professionals, we are focused on one thing, photography. Not a day job that demands most of our time. (If you have a family, then you have even further demands on your time and that leaves you less to work on being a photographer, too.)
As professionals, we are members of several different organizations (I think they were called unions earlier) that help us to accomplish our goals and be the best we can be. They aren't secret factions, but the membership is restricted and limited. Why? Because the membership in these organizations are faced with similar needs and issues and that keeps the focus and subject matter on what truely benefits the members. It wouldn't benefit members of a professional guild to have seminars on basic camera courses, basic photography, and lighting...you should already KNOW these things before you open a business. This is what the amateur and part-time people need and it would take away from the value of the Professional Guilds and organizations. Those professional organizations are TOOLS for people earning a living in this industry. Not to help teach someone how to take pretty pictures.
To go even a step further, as a professional, I offer many assurances and peace of mind others only working out of their homes and part-time do not. Ask yourself, would you give a photographer several thousand dollars of your hard earned money (5-7K) for portraits if all you had was a cell phone number and the address of a local Starbucks?

Hell no you wouldn't. If he/she skipped with your money how would you find them? If you are dealing with Professionals with studios and comprehensive insurance coverage you at least have a point of reference that you can turn to if there is an issue. I have clients that spend upward of 15K on prints from a familiy protrait session...You don't give someone that kind of cash without assurance that you will get what you are paying for.
The undocumented "businesses" you mentioned, well, that is all to common, but extremely dangerous for the business "owner" and the clients. Most of those are illegal as most people that live in neighborhoods with HOA/ POS's restrict running a business out of your home. Once caught, you are really faced with a mess and that mess can spill over onto the client. (Talk about a situation I never want to be in.)
The problem with photography...ANYONE can buy an expensive camera and call themselves a "professional" photographer because someone told them "Oh you take such wonderful pictures!" (when actually someone was just being nice...it is called human nature) and they have received some pay in the past. There are no licenses, restrictions or requirements so therefore ANYONE can be a professional photographer. This fact alone is the reason 85% or more of the people that open a photography business can't make a living at it. They are in the
Photography business when they should be in the
Business of Photography. You have to be a sucessful business person (or have one managing your business) before you can make a living at photography.
So the profession of Professional Photographer isn't a thing of the past. Honestly, there probably isn't that many professionals, earning their living on this forum, not for fear of it, but simply because they do not have time to operate a sucessful business and blog, post in a forum and spend time educating someone wanting to learn photography. They have to pay the bills! They focus on other forums (paid membership) that addresses the issues they need addressed and that helps them run a sucessful business. As part-time and amateur photographers, most would see that expense (paid forums) a waste of money.
CJ