(This is really more Galileo than it is Newton, but that changes little.)

Lith demonstrates how Newton too requires us to believe in certain concepts (like inertia) which are unachievable in the Universe. This is taken as a measure of crackpottedness (cracked potty -hood?). In particular, it is argued that telekinesis is in a similar state: believing in it means believing in concepts unachievable in the Universe.. I would counter that Lith is of course correct regarding unachievability of zero force exerted, but is drawing the wrong conclusions.

Newton's laws are an axiomatic definition of force. Force is a somewhat imaginary construct: for instance, it is invisible. But so is length. Instead, Physics (being, after all, the science of measurement) makes do with telling us how to measure it. You measure length by using a piece of string; you measure force by using a spring (better methods exist for measuring both, of course; switching to a better method just requires callibration against the old method, and a demonstration that the new method is indeed better). In particular, to measure friction, you just attach a spring to an object, tug at the spring, and note that the spring extends. Newton's laws give a framework for understanding why a spring would indeed measure force. But you may think of it backwards: giving a mathematical theory of how springs behave, it is easy to reformulate it around a new concept of "force". This is essentially what Newton did.

So what's with inertia? Why do physicists insist on the "fact" that "objects continue at a constant velocity if no net force is applied", when we all know that force is always applied?

It's just Newton's first law. Newton claims that there is this measurable thingy called "force". Zebulun wants to know how he might see it in action. Newton claims that force is what changes velocity; force is the only thing that can change velocity! Zebulun keeps seeing velocity changes, so that settles the question of seeing force in the world. But it raises a host of new questions: for every velocity change that Zebulun sees, Newton (or some other physicist) has to find a force! And these forces must "explain away" the velocity change using Newton's laws; no new laws are permitted (even Relativity keeps Newton's laws intact, but changes the interpretation of some of the quanitities appearing in them).

Besides, you can see an empirical demonstration of the first law. You can't have zero net force acting on an object, but you can reduce the net force arbitrarily low. It's called measurement. It's not accurate, but that's life. And indeed Newton's laws explain everything they claim to (or at least, they did, if you apply minor corrections for Relativity and don't work on the very small scale, where measurement artefacts (aka Quantum theory) show up).

Contrast this with telekinesis. Whereas changes in velocity are everywhere to be seen, telekinesis is nowhere to be seen. Occasionally one is told that TK may be observed at some lab. Invariably, it turns out that TK will only be seen under extremely restricted circumstances (the right person has to operate the measuring apparatus, the right person has to be tested for TK, it has to be done at the right lab, and the right audience must be present, or they will broadcast negative mind energy and negate the TK effect). The Newton vs. Zebulun Metaphysical Catfight takes place in the lab: all effects are real and easily observed; the question is if a single mathematical theory can explain them all. The TK vs. Science Metaphysical Catfight takes place in our imaginations: the existence of none of the effects has even been demonstrated, and yet TKers want to talk about their theories of how it all occurs.

No contest.