The majority of people disagree because it is a truly cosmically stupid and ignorant statement. Tell it to Saint Ansel whose workshops inspired hundreds of photographers over many years (yours truly among them).
The fact is that in any field of art, supporting yourself solely by selling your work or talent is very rare and difficult, and depends as much on luck, contacts, and self-promotion as it does on the quality of your work. I mean, look at the dreck being sold for large amounts in some galleries in NY and elsewhere, or the many photographers making a living with "calendar and greeting card" crap.
Many highly talented artists teach because they love working with students. It can also be a way to pay the bills to allow you to pursue your passion.
It's unfortunate that you did not have better teachers.
Peter, at first I thought of underlining or making bold the points I was going to raise, then I decided it wasn't going to look pretty, so I won't.
The more elegant way is to say just "thank you" for, in fact, simply restating my case for me, which is, in essence, that yes, making it as career in photography is tough, and only if you can't hack that full-time, do you seek alternatives to enable the paying of the grocery and/or light bills, as Saul Leiter was wont to say.
Regarding the anointed one: if you read his "Letters, 1916 - 1984" you realise that far from making it big in professional photography he spent most of his days as a photographer pretty much broke. He also wasted a lot of time doing what I'm doing here: having exchanges with other photographers. If you ask me, which you have not, I'd suggest a part of his problem was taking up photography instead of staying with his first love: music. (Regarding photography in general, it has often been said that photography is something some people take up only after failing at everything else; I defeated those odds by making the jump at the first opportunity and thus robbing a demented Fate from beating me to it...)
The 'saint' began to 'make it' in relative old age, via the politics he embraced within the Sierra Club that led to a higher profile in 'conservation', and then the even more important intervention of an angel, a gentleman who took him into the gallery world. If you do or do not think of the gallery world as professional photography, I do not know; for my part, it's not. Not even remotely.
Rob
P.S.
Just noticed the crack about my having better teachers: if you look at my website you'll find that I dedicate a line to one of mine: Barbara Farr, who was the best English teacher - or teacher of anything - that I ever encountered. Photography teachers? I had 'em forced upon me too, unfortunately, and I walked out when I realised them to be totally irrelevant to my life, desires and needs; they were even less informed of where I wanted to journey than was I. It's been the experience of every successful snapper I have met - can't vouch for the others. Photographic teaching begins and ends with the mechanics, possibly now the electronics of the business. That bit's simple: the problem, when there is one, resides inside the head of the snapper.
Good teachers certainly do exist, but then the good ones don't sell snake oil; they don't make you promises designed to lighten your pocket rather than to enlighten your mind.