I am ever so grateful to Bill Westmiller, whose comments are marked "BW: ". The quotes marked TSW are from "The Scientific Worldview" and my comments are marked "[GB: ".
TSW: "It is, of course, impossible to know for sure which of these possibilities really exists; we can only assume one or the other."
BW: I've noted my distaste for the idea of one arbitrary "assumption" being as good as another. If the yardstick is omniscience, then we can never know anything "for sure". An hypothesis is subject to evidential and logical support, which is either unmitigated or mitigated by contrary evidence or logic. In effect, you've made a strong attempt to *justify* your assumptions, citing evidence and applying logical principles. That's good. It doesn't mean that your conclusions are *absolutely true*, but you're attempting to persuade the reader that they are something close to an "unmitigated truth".
TSW: "The more one saw of the macroscopic world, the more one was impressed by its immensity; the more one saw of the microscopic world, the more one was impressed by its inexhaustibility."
BW: I don't think they're equivalent.
The Big Bang theory has been falling apart ever since it was proposed. The discovered dimensions of the known cosmos were "impossible" without tagging on a crazy "Inflationary Epoch" of FTL [faster than light] separation. The acceleration of remote galaxies was "impossible" without throwing in the silly "Dark Energy" pulling power. The temperature of the Cosmic Microwave Background was "impossibly" hot in comparison with the theoretic predictions.
To my mind, all of these discoveries establish that there are huge gravitational bodies in adjacent cosmos, far beyond our light cone. They are attracting the most remote galaxies and generating hot cosmic rays. Therefore, the evidence for infinity is significant and there is no contrary evidence. Aside from the preposterous, mystical origin of "something from nothing", the Big Bang theory is dying with a whimper.
BW: On the microcosm side, the evidence is different, coming in staged phases. Inquiry has moved from the "basic elements" of fire, water, etc. ... to the classes of metals, gasses, liquids, etc. ... to the atoms ... to subatomic particles. Each of those discoveries identified distinct incremental steps in the microcosm, rather than continuous homogeneity.
TSW: "[Bruno and Newton] retained the legacy of atomism, which, without a doubt, presumed microscopic finity.
BW: And they were right in advocating a new incremental step of causation for the observed classifications of material properties in like objects. The atomist theory was an unmitigated truth, with no contrary evidence, until the discovery of radiation and the next incremental steps toward identifying a new layer of coherent material components. They were wrong about "indivisibility", but not atomism.
TSW: "... microscopic infinity logically implies macroscopic infinity and vice versa."
BW: I don't think it logically follows. If anything, the concept "infinity" is an abstract ideal. If there is good evidence for a macro-infinity, it says nothing about micro-infinity: nature doesn't have to conform with human inclinations to assume one attribute necessarily applies in an opposite "direction". Remember that your "micro" and "macro" are relative terms: much bigger or much smaller than US humans. But, we aren't exceptional to nature ... at least not by virtue of our size.
TSW: "This follows from many of the previous discussions, particularly the one on 'spacetime' involving the opposed concepts of ideal 'solid matter' and ideal 'empty space.'"
BW: Simply because there is a conceptual idea does *not* mean that it must exist, nor that it *cannot* exist, in nature. The idea is either true or false, based on evidence and logic. For example, on the macrocosmic side, nobody contends that our universe is "solid matter", even if they imagine a peripheral "empty space". On the microcosmic side, nobody contends that there are no gravitational forces (= energy = matter in motion) "between" atoms, nor even among subatomic particles. The universe does not have to conform with the Thesis > Antithesis of dialectics.
TSW: "The resulting assumption of infinity ... is the only form compatible with causality and uncertainty."
BW: I've pointed out several instances in prior assumptions where infinity was irrelevant.
BW: Causality says there is at least one cause for every effect. It doesn't require a specific number of causes ... much less an infinite set. The speed of light is a well established fact, meaning that objects beyond our light cone *cannot* cause any local effects. Until science demonstrates or discovers FTL, causality cannot be infinite.
BW: Uncertainty has nothing to do with any kind of infinity, at least not in Heisenberg's proposition. Some forms of observation entail modification of the objects being "viewed". That's critical on the subatomic level, but irrelevant for any large object emitting or reflecting light. Nor does the Uncertainly Principle affirm or refute the existence of an infinite microcosmic progression of discrete steps. It simply says there's a problem with observing them.