I've been thinking about this topic for a while, and a few posts in the last couple of months have discussed related issues, so I thought it a good time to raise the topic.
First, a clarification - I see no qualitative difference between amateur and professional, merely how they make their money. In the LF world, I have sometimes even hazarded a guess that amateurs are frequently producing better quality work (though lower in volume) than professionals, because they want to get things right and are less bound by practical considerations.
'Less bound by practical considerations' is an important point in this ramble.
I also don't have a great contact with the fine art world, or indeed with that many photographers, so keep that pinch of salt handy.
Stock photography is dying as an income to many individual photographers. Some photographers I know who make money from workshops, print sales, book sales, and stock, have seen a drastic decline in stock sales, and have started focussing more on workshops and print sales to make up for it. They wonder how friends in the travel photography business actually survive. The main cause seems to be saturation of the market, but a related cause is the increase in amateurs registering with online stock agencies. They don't care how much they get, just the thrill of being published. They might not put a lot of work online, but there's a lot of them. Doing a web search recently on a major online stock site, I was amazed at how many people I knew who were selling a couple of dozen shots.
In the fine art market, I've seen more people with 'normal', reasonably well-paying jobs, who buy nice equipment and enjoy spending their free time doing photography, decide it's time to get some print sales. Money isn't a factor - they don't need to feed themselves or cover equipment costs based on the sales (they would have bought the equipment anyway).They price in one of two ways: price low, to aim for maximum print sales; price high, because they consider their work as good as Gursky, Shore, Muench, Sexton et al. but maybe need to temper the price to reflect some degree of market reality. They don't care if they only get a few sales, if that. High price gives credibility.
I've seen people in the former group who price barely above material costs - paper and ink etc, not taking into account printers, enlargers, cameras, film etc. And those in the latter group who refuse reasonably generous offers for work, because it's clearly 'worth more than that', even if sales don't support their pricing.
I'm curious how others view the amateur vs professional divide, and whether they've come across odd situations, and how the future looks for the full-time professional. People 'undermining fellow photographers/the profession, by charging too low'. They show society the 'real worth' of work by charging highly.
This isn't really the same issue as grain dumping eg, because dumping is sometimes used as a tool to damage competition -the high and low pricers genuinely don't care about cost.
On the whole, I don't care if eg a professional wedding photographer with a family to feed (for added emotive value!) loses work to an amateur who does a few jobs just to cover film/printing and enjoy the publicity. Provided the amateur is doing good work and can demonstrate appropriate experience/backup, your other financial commitment simply price you out of the job.
I think this is more of an LF issue, because it seems the proportion of amateurs making a bit of money esp in fine art, increases as you go up the formats. I suspect some of the full-time pros will be priced out of the market, but I don't see that as a bad thing, just a change.