As with many of these kind of debates, the real answer is "it depends on the kind of game".
A single player story driven game such as Mass Effect or Dragon Age cannot be done free to play. Or, well, okay yeah you probably could do it, but it would not be a fun experience. Imagine getting the briefing for the next mission, with a message "pay £5 to unlock". Or having to spend hours away from the story, grinding XP to unlock a new weapon.
If the £40/$60 singleplayer part of gaming dies, I'll probably buy about 2 games a year.
Free to play can work in multiplayer, but it can also be abused by the developers, so we have to be careful as consumers to not allow the concept to be pushed too far. Paying for hats that don't affect gameplay is okay. Paying for weapons that make you more powerful is absolutely not.