What's up with the on-screen buttons dogma?

I've been impressed by the sheer number of people calling the lack of on-screen buttons a deal breaker. Why is it so surprising? Because it doesn't make sense. There's not a single advantage, unless you consider losing part of your screen an advantage, to on-screen buttons.

Possible argument 1: "Are there when you need them, not when you don't."

You need those buttons all the time. ALL the time. That's the reason they take a permanent space in your screen, except when you watch a video or see a picture, but this doesn't represent an advantage, because you get a fullscreen experience with hardware buttons ANYWAY. Yet, it implies a loss of content on all other instances.

Possible argument 2: "It makes the phone smaller".

Except it doesn't. The Galaxy Nexus still has a large space under the screen for its notification led, also there for aesthetic reasons, and because it would be less comfortable to hold.

Possible argument 3: "It adds consistency".

It doesn't change anything. The menu button was a design mistake, because it depended on the specific app opened, and there was no way to know whether there were extra options or not, other than pressing the button. Same with search, you didn't know if the app supported search until after you pressed the damn button. This isn't the case with multitask, back and home, their function doesn't change because of the app currently opened, and its entirely predictable what they will do (well, not so much for back). In fact, those three buttons are just simulations of hardware buttons, that's it.

Is there any actual argument for the use of on-screen button for those specific three buttons?.