"I decided to be a determinist because it's just easier. I can stop analyzing "why" I did this or that and simply accept the fact that my willing at any moment is the confluence of countless prior influences, conscious and unconscious. In a clip of Christopher Hitchens discussing global warming, notice how the phrasing of the question––"missing the boat"––leads to him using the word "boat" in his reply (or should I say leads him to using the word?). If challenged about his lack of rhetorical ingenuity, Hitchens would probably just shrug and say, "Well, there's determinism for you." Determinism, therefore, is true because it allows us to mesh most naturally with our environment."
I will suggest the following, though: the above comments make what I think is the deepest ontological error in determinism, namely, the claim that there is some puny, passive subject, which is constantly influenced by its environment, yet which does not add anything to that environment. The "self" in determinism is like the beam of light reflected in a mirror: a reality which allegedly only exists at its entry and exit points in the visible spectrum.
Also, while there is some truth (!) in the pragmatic thesis that "the true is the workable", since goodness is an analogue of being and both are unified in truth (and vice versa in all three directions), the very difficulty of "working out" certain interrelated claims is a sign of their truth (quantum mechanics, trinitarian theology, the "place" of the will [as if it were a spatiotemporal entity to begin with!], etc.). Further, the harmony, the functional resonance, which we experience in grasping the true does not mean the true is the useful; for some things are known to be true by their beauty, a beauty which of itself preempts pragmatic lechery. What is "it" good for? Shut up, philistine, and accept that its pragmatic vacuity is precisely the sign of its alethic dignity. A remaining snag is how to meet the utilitarian claim that even the "purely beautiful" is 'useful' in the utilitarian sense. Then again, that seems to be so much a concession to the classical view of beauty qua truth qua goodness as to be more a surrender than a challenge to metaphysics.
P.S. A clue that pragmatic success does not amount to truth: doping in the 1980 Olmypics.