Because you are asking:
1) How do you change the minds of informed audiophiles with information contrary to their prevailing views?
If I knew the answer to this! Audiophile dogma dies hard, I think you are already doing what you can, allowing for fairly painless home auditions. Very precise, clear, measurements can help (see 3 below).
2) Is framing this as a passive vs. active debate even useful or effective?
This depends on what you want to make/sell. Of course LDR does not have to mean passive. I suspect that you would find a very good market for an LDR preamp with a really good, discrete, MOSFET unity gain buffer at its output (some might be OK with a diamond buffer IC). There is no question that some source/amp combos need additional current drive (not gain though) to achieve good dynamics. The problem is a passive will not suit all systems. I prefer to view gain as a separate issue, too many audiophiles do not address proper gain matching in their systems and are throwing away performance.
3) What are the key issues with preamps and does the LDR preamp address these or not?
Inserting any component results in losses. I prefer source-amp direct connection as long as the source has enough current drive to achieve good dynamics. As I DIY, I just make sure my DAC has a robust enough output stage, and good gain matching, and I can then use digital volume control and eliminate a box and interconnect. I also prefer single source systems, eliminating any switches from the signal path, as switches can be heard, as can an extra interconnect.
Volume control implementation is a critical design element of preamps, no question. So, if LDR really is better, than say, Shallco switch stepped attenuators with 0.1% TX2575 resistors, then you have a benefit-but without publishing very precise measurements from an AP sys 2 of a passive with the above two volume controls there is little evidence to prove that the LDR is better. Let's see a comparison of noise and distortion spectra at: 0 dB, -4 dB, -8 dB, -16 dB, -32 dB, -64 dB.
In the best preamps, active or not is not really the question, as the best active stages can be so close to fully transparent (distortion levels below the threshold of audability) that there is no downside to having an active circuit. Implementaion of PCB layout, input switches, and volume control are going to be the defining aspects of preamp "sound".