No objective test can establish the existence or purpose of dark matter or energy, either, and yet scientists are still imagining that they must exist.
Not quite true. It is because of objective evidence that both have been hypothesized. And, in the case of dark matter, there is a LOT of objective evidence pointing to its existence. What is missing is the determination of what dark matter is composed of in terms of elementary particles. But, using objective evidence, we can map out where dark matter is and test various alternative explanations (which have, up to now, all failed).
For dark energy, again, it is because of the objective evidence of accelerating expansion that Einstein's cosmological constant was revived at all. We are still very early in terms of looking at alternative explanations of the data so far, but all that we have is consistent with that cosmological constant (now called dark energy).
No objective test can establish the existence of a "singularity" prior to the Big Bang, and yet lots of scientists imagine that it must have existed in some inexplicable form.
The singularity is predicted based on models that have massive amounts of evidence in their favor. Those models have been extensively tested.
But, in this, you are correct. There are more inclusive models involving quantum gravity in which there is no 'singularity' (although there remains a very good approximation). The problem is that none of the quantum theories of gravity is currently testable (a technological issue, not a fundamental one).
No objective test can explain why or even how energy behaves as it does, and does not behave as it doesn't. And yet so far as we can tell, this control is and has remained absolutely consistent in a universe where little else does.
I have no idea what you are talking about here. Our current theories are quite good at explaining how energy (and matter) behave. As for 'control', the only 'control' I can see as relevant here is the laws of physics. And yes, those laws, as far as we understand them, work quite well.
Or perhaps this kind of materialist bravado is getting ahead of itself.
If you have a testable alternative, let someone know.