Hm, Killzone and inFamous had options to lock it to 30FPS.

Are you sure they had no judder with unlocked framerates? Some people are more sensitive to judder than others, I prefer unlocked 45FPS to 30 locked, but others prefer 30 locked.

Its not debatable, its fact. Every game benefits from 60fps, even though some more than others. 

The problem is that not every gamer is tight enough with their gaming to notice. I honestly struggle to understand those that say there isnt a difference because for me its a dramatic difference. I will sacrifice particle effects, AI, fidelity and polygons if it means i get smooth, responsive and fun gameplay.

10 years from now when you play the game the eye candy will be outdated and mean nothing while the 60fps gives you a timeless classic based on smooth and fun gameplay.

Stable 30 with glorified features is better than 60 fps that looks like shit. That is my preference though.

60fps is an unnecessary luxury

Of course 60fps itself is inherently better than 30fps, but the debate is what's better between 60fps vs 30fps/variable + [x]. For many people, the latter is often the better choice. For many others, the former is the way to go. It's mostly a matter of preference.

Knowing that you can't please everyone, it's best for the developer to decide what they think is best for their game and the audience that will be playing it. All ND is really saying here is that if they believe [x] adds more to the experiences for their players (though they don't specify what), then naturally they're going to pick that.

No, they're getting sued for marketing the simulated 1080p (2 interlaces 960 x 1080 frames with a predication algorithm to properly sync the two) as native 1080p. The debate right now is what "native" actually means, since the standard definition puts Killzone is somewhat of a grey area.

To be honest the whole situation is silly. Regardless to if they win or lose, GG and Sony should have been open about the technique from the start. It's a damn cool bit of tech, and something many games could benefit from using (though the prediction algorithm needs some work).

Honestly I want 30fps and something closer to the initial reveal. The demo looked great but not the leap I was hoping for.

Having said that there are 28 numbers between 30 and 60 and it shouldn't be 60fps or nothing. I'm playing around in Unreal engine 4 at the moment and 35fps is even notable over 30fps.

InFamous had visible judder before the day one patch, but it solved it. Killzone never had any problem for me. I normally notice judder easily, my aging PC GPU (GTX 650) has some troubles with modern games and sometimes I end up with games that flutuate from 30 to 40-50 fps and it judders a lot (V-sync isn't an option since it normally has a big hit in performance and that's something I can't afford). Thief on PS4 and PC was a stutter festival, as an example. But in some months I will get my 970 and everything will be nice and smooth again.

About locked vs unlocked, I prefer an unlocked fps if, and only if, it comes with a v-sync solution that avoids stuttering. I can even live with small tearing, but stuttering is a deal breaker for me. So the order would be: unlocked with good v-sync > 30 locked >>> unlocked with tearing  >>>>>>>>>>> unlocked with stuttering.

I experienced the exact same. When directly switching between the two, the difference is quite big. However If you're only offered 30fps to begin with, your eyes except it as a smooth image. 

I wouldn't mind 60 fps but that is a luxury and I'd rather have them create it at 30 fps rather than having to downgrade the rest of the game's performance just to reach a higher fps.