One of the eaglejet programs places guys in the right seat of a B99 at Amflight. It's not taking anyones job away and you're not "working for free" cause you're not really "working". The plane can go without you, and normally it does. In fact, you can be bumped for freight.
Is this time valuable? Maybe a little bit under certain circumstances. But I'd put time as a CFI as more valuable, and right seat timebuilding programs shouldn't be a substitue for that. Certainly, 250 hours is way overkill and not necessary.
I agree that nobody should ever work for free. It's not good for the profession and gives management bad ideas. My test for these things is "can the airplane go without me". If the answer is yes, then you're hardly taking a job away from anyone. If the answer is no, then you should be paid.
Somebody will say "well, how can you log the time if you're not a required crewmember". That's a good question for eaglejet. But I believe Amflight has something in their ops specs that allows these guys to log the time. I know they have been doing this program for years.