Horn based loudspeakers why the controversy?

… Most horn systems are physically large, and like a lot of other large speakers, they deliver a "big" sound. The sound seems to fill up a large volume of space and envelop the listener. I like this quality a lot. When one listens to tiny speakers, even when they play quite loudly, one can sense that the sound is coming from a small source and it does not seem to have realistic scale.

I wholeheartedly agree with the above. Being ’enveloped’ (a very fitting term here) by sound the way large horns can do while providing proper-ish scale is what really sets them apart from most others speakers, I find. Another aspect that is inherently linked to this sensation is that of effortlessness; it de-stresses the sound in a way that is both relaxing and more believable. Smaller, direct radiating speakers can sound "large" in a different, spatial way, but they don’t load the listening space in the same authoritative, solid and room-lock kind of way.

The most realistic sonic presentation of an orchestral piece I’ve ever heard came from a really good movie theatre system employing horns.  Eyes closed it was astonishingly like listening to a full orchestra!

Non sound reinforced (i.e. simply acoustic) shows are far different from otherwise, and an acoustic quartet certainly does have "startling dynamics" to the musicians playing the instruments, and maybe anybody within 10 feet of them...but that's about it. In my sideline as a working soundman I've mixed hundreds of acoustic shows that DO have a clean system to run through...from the Baltimore Consort to John Renbourn to various jazz artists, and I love actually hearing those otherwise lost dynamics...through horn loaded systems of course (or phased arrays which also work). From a single large diaphragm condenser mic (classicial trios and bluegrass ensembles mostly), to multi miked whatever, the passion and dynamics of well played music is better when people can hear it, and well made generally horn loaded speakers make that possible.

I’ll agree with most of the above, and most of that is exactly why I dislike horns. I’ve never attended an acoustic performance that sounded anything like what I’ve heard through a horn system.

I don’t know the horns you’re referring to here, but like any speaker (principle) a given iteration could be less representative of live, acoustic sound, just like another could, conversely, be more favorable. What’s more surprising to me is reading this:

A quartet doesn’t sound room filling or enveloping. It doesn’t have startling dynamics. It doesn’t sound huge.

My first inclination is thinking you’re willfully obstinate here, because it goes quite contrary to my own impressions. No "to each their own" here, but more like: really?

The scale and imaging I find in the live performances I’ve heard is much more like the dynamic speakers I’ve heard than any horn.

Why I’d have to reiterate my prior question about which horn speakers you’ve heard, or which live concerts forms the basis for your statement.
On second thought I’m wondering whether you’re mostly referring to the spatial aspect of the sound, and that this may be where your preference lies with speakers that aren’t horns, if it’s even a valid distinction between them. People may have different "filters" in regards to what they’re listening for at a live, acoustic concert (or any auditioning event for that matter), that could lead to a variety of different descriptions about the sonic culprits each individual is hearing.

I’m sure I’ll be jumped on because I’ve never experienced a live acoustic performance that’s sounded anything like what horns do. I’ve never heard any violin, clarinet, or kettle drum really sound huge or enveloping in any venue.

I’m more confounded than aggravated by your stance, and the part regarding "huge sound" needs some explanation: big horn speakers sounding "big" to me is about having proper scale and emulating a realistic sonic size, rather than sounding "huge" per se. Good horn sound is also about proper, uninhibited presence.

Once at a classical concert I attended (can’t remember which, but it was rather large scale, symphonic), I was thinking more elaborately about the problem of remembering how a live concert sounds, and how to recall that in front of the stereo at home for comparisons sake. It then occurred to me, at the classical concert, to close my eyes and in a way turn things on its head; I vividly imagined I was sitting in front of my stereo in that very moment, as a simple mind trick, and that turned out to be quite revelatory to me being that I suddenly realized what a live classical concert sounded like - in front of the stereo, no less! To me at least "bringing the home stereo environment to the live concert" is much more effective than taking a live sonic memory with you home. That said not with the intention of being lecturing, but simply a mere anecdote on how I’m trying to cope with live, acoustic sound as an ideal in a sense for what to strive for in reproduced form.