In my small experience, The people giving out freebies are usually not versed in that industry, so they are trying to get expirience that way. There is always a constant wave of people who are doing some work for free, or on the cheap.
As their gear gets better and they get more experience, they realize they cannot survive or progress this way. They will weed themselves out I believe,
also everyone needs to start somewhere, everyone who shoots weddings did a friend or families wedding for cheap or free somewhere along the line. So when you hear stories about this, you have to think to yourself, if this is a beginner, then its not even close to apples and apples.
The first 2 weddings I shot were friends and family, I did them cheap and in exchange for memory cards, I learned a LOT and also they were in no position to pay anyone anyways. These weddings were in cheap hotel lobbies and dry old parks at 12 noon. These weddings are just fodder for expiramenting and learning. No beginner photographer is going to land a destinations wedding for 300 -500$ it just doesnt happen, nothing to worry about there,
With pro -sports shooting the official guys with a copyright to control (security) take care of beginners, if you have the clearence to shoot your in good hands, if not your not making any money anyways.
with horsey stuff, and little league stuff and dirt track racing, all un-sanctioned stuff, its prob a lot more tricky. People dont know who to buy from, they just can see the results and prob your equipment, I would dress professional, have examples of your best work and be courteous, this should set you apart from the amateur easily.
So, in actuality not everything a beginner gives away robs anyone of anything.
In some cases it can even help. it will vary per industry and location, but for example the beginner giving away weddings for cheap is 85% most likely shooting stuff either noone else wants, and thats because the B&G cant afford more then 300$
Instead of complain about this we should be improving our work and making sure we are getting noticed by the right people and stop worrying about the slush market.
Educating the general public about quality photography is more noble a concern I think.
Just thoughts, didnt mean to go on a rant... lol