This is definitely a recurring debate I keep seeing, but it's funny how we've been here before. In the early days of shareware it was common to see stacks of games on 1.44 floppies you could buy for $5 to try the first episode (I played the hell out of Halloween Harry that way); the only difference is instead of paying for pure content you're paying for additional enhancements to the freely accessible content.
The real question in this debate though is price tiering. What's the sweet spot for consumers to buy a F2P game on disc that lets it compete with full-priced offerings or subscription-based mmos?
Perceived value is an issue the F2P market is still evaluating how to tackle. Right now the problem is an attitude of 'oh they're giving it away for free, so it must not be any good.' Yet F2P games can't compete with console or full titles, so there has to be a unique price structure specifically for these types of games. Personally I think it's a matter of time before one of the many game operators figures it out.
Take your favorite F2P MMO. What price would you feel comfortable paying for it in a store, in a proper box? What price would it be a steal at? What price would you pass on it? These are the eternal questions