[kijin]

There are different kinds of "testable".

Some theories are so easy to test, a 4th grader in her science class can test it conclusively in half an hour. We don't even question these theories anymore, because they've been set in stone for centuries.

Some theories take millions of dollars and several years to test, but they're manageable by large research universities and governments. At the very edge of this range, we have things like the Large Hadron Collider testing the existence of the Higgs boson. That one actually cost a few billion dollars and several decades, but we could live with that.

Some theories will take trillions of dollars and several centuries to test. Perhaps it will be quadrillions of dollars and several millennia instead, or even several million years. Right now, we don't even know what kind of technology we will need to test string theory. Perhaps we'll need to evolve into something else before our brains can even imagine what it would take to test it. But eventually we'll get there, if we learn to accept that science is bigger than all of us and stop being so impatient.

The difference between these three kinds of "testable" are quantitative, not qualitative. It just looks qualitative because the quantities involved are so huge. But if someone cannot grasp the idea of a theory that takes aeons to develop and test, I don't think they're qualified to judge the merits of theoretical physics.