What about what actually happened with Duels though: a free to play game that was unplayable for about 2-3 seasons? Did you stick with it anyway? Did you ever justify that decision because the game was 'free?' Do you think WotC doesn't owe you a high-quality product, simply because of the price?
These are all things I've heard from ftp boosters... all the while the developers are laughing at you, because in order to play the game for 'free' you are earning coins who's cash value are far less than a fair wage for your time, you'd make way more delivering pizza or working at McDonalds. You think you are getting the game for free, but what's really happening is that you are slaving away to make the game playable/better for the people that actually pay. And at the same time, the people that actually pay are getting screwed too, because the game is way overpriced for them (either that or the game fails).
Fwiw, I get the whole try before you buy thing, but there are ways to offer that without making the game ftp too. In fact, a lot of great pay games offer demos, and trial periods... None of this is unique to ftp. The only thing unique to ftp is that the developer can't be held accountable for the game being terrible, because, as you said, it's 'free.' And of course, if you decide that you really do like the game, now you're getting screwed as described above.
Maybe I'll get lucky and they'll offer a ftp and a non-ftp version, some games do that - here's hoping they do.
p.s.: MTGO is terrible. I'm looking for a way to play mtg, not for a way to make my eyes bleed.
I'd rather play paper magic.