That's everyone's mindset, but it's not true. And it's that mindset that keeps us from moving forward. If you have an unlocked (preferably pentaband) phone, you have a lot of options. Sure, in terms of major carriers, you're looking at either AT&T or T-Mobile, but there's a plethora of viable MVNOs that offer great deals. And in terms of "paying for the privilege" to leave a carrier, that is only true if you've signed a contract...I can leave whenever I want without paying a dime.
If we as consumers had demanded (and expected) such freedom of movement between carriers, maybe we'd see more reasonable price competition and we might not have ended up in the LTE frequency mess we're in now.
You have a lot of MVNO options now, and you don't need an unlocked phone, though U.S. MVNO's generally are limited in what they offer as opposed to the carrier whose spectrum they are using.
I don't disagree that it would be great if people could move around at their whim, but the U.S.wireless companies operate in a completely different manner than most of the rest of the world, and there are fewer options.