How many Pro's put out workshops where people pay good money for them?
But generally you learn a lot in these situations.
Instead of the participants paying hard cash, they are exchanging menial labour for an on the job workshop.
Though in these arrangements the amount learned will very often depend on the abilities of the main. But you do get to actually feel how much work is involved on the day.
Second shooting, if your main hands over to a client, anything the second shooter has done, then it should be compensated. If the second shooter has nothing the main wants to use and no fee was negotiated then I don't see why they should get paid, as they have exchanged time for potential portfolio work. Which could lead to paying clients.
Many pro's pay second shooters and assistants as a rule, but these photographers very often get to pick second shooters and assistants, who have already gained experience and have portfolios and references.
Shooting a wedding for free, is always to gain experience and portfolio work, as clients won't even risk you for $100 unless they have seen some previous wedding work. You gain more portfolio work, and learn first hand a wedding workflow from beginning to end. With no exchange of money the free photographer cannot be sued. Very important, as mistakes will be made and a court will rule something is only worth what has been paid for it.
I think working for free is the first rung of the ladder in this industry. Being free protects the newbie photographer from major repercussions if mistakes occur. Though a sensible person will still get insurances for at least their equipment.
Working for free as an "intern" whether it is a weeks full time work or 6 months, with the promise of paid work at the end is nearly always exploitation, lots of rather large companies use this tactic, have an intern for 6 months, and then at the end say "oh no, sorry.... you didn't get the job" only to already be pulling in the next intern.
I haven't heard that in the wedding industry, but I have witnessed it in the larger business world. TV, radio, clothing, even office work for solicitors, the list goes on...
The other stupid one is apprenticeships, you at least get a wage, but it is very often in the building trade, getting paid a lot less than minimum wage for back breaking work.
Taking a few unpaid jobs to build a portfolio, to lead to paid work and a business of your own is one thing because it is on your terms.
Chasing the carrot on the end of the stick, that someone else is holding, only for it to never be intended for you, is exploitation.