Horn based loudspeakers why the controversy?

Horns were virtually ignored by the "high-end" journals like TAS and the Stereophile back in the day. The transition to solid state probably didn’t help either, given that a lot of early sound state gear could be rough on the ears. Size mattered too- I had an older friend while I was finishing college who ran a pair of old K-horns with then already vintage Marantz tube gear and it sounded pretty good. (At the time I was using the original Quad ESL and Audio Research tube amp and preamp).
The notion of vintage horns like WE, RCA, JBL, etc. seemed pretty removed from the collective wisdom being preached in the era when I started fooling around with "serious" gear--the very early ’70s. I think it wasn’t promoted, manufactured or sold much in the States for consumer audio, and certainly wasn’t given the imprimatur of the authorities of the day (back when reading Harry Pearson and J.G. Holt was meaningful-i think people are far more skeptical of reviews and reviewers today, which is a different subject).
I know there were hardcore horn enthusiasts in the Far East. And perhaps a few on the fringes here in the States.
What products revived the horn? Avantgarde was certainly one; there are probably some others, of recent manufacture within the last ten years, along with greater awareness of vintage equipment, like idler turntables and SET amps. (My Avantgardes didn’t really sing until I got a pair of Lamm ML2s).
A hybrid horn system is still a challenge--matching woofer characteristics to the mid and high frequency horns. A full horn system including bass horns is not only large but unless you are DIY, costly. (Even DIY is costly if you are using vintage or more modern high end compression drivers).
I know some people that visited me over the years were surprised that there was no "shouty" ear bleeding aspect to the system--part of it was set up, and a lot had to do with associated components. I’m not sure how effectively horns have been demonstrated at hi-fi shows after their modern resurgence (I don’t go to audio shows much any more).
I also don’t listen at crazy high dbs. In fact, I can get a lot of information at low volume levels, but the bass (I supplement with 15 inch servo woofers, not ideal, but cost-effective) doesn’t really come alive until the system is played at "normal" listening levels. I think the dynamic capabilities aren’t just about "peak loudness" but the so-called ’jump factor’- the ability of the system to make those dynamic swings effortlessly. As a decades long Quad listener (still have ’em, just got ’em restored), I’ve always been about the midrange first- open, non-grainy, not "reproduced" sounding. Horns give me that. The Quads are easier to set up but have even greater limitations. I love both.
I’ve heard very convincing conventional coned speakers- such as the Rockports, driven by very substantial amplification and a good analog front end. Such systems do some things better (at least in the bass region, unless you have horn woofers).
It’s all trade-offs somewhere. Pick your preference. I’ve been extremely happy with my horn system for the past 11 years, and know that I could do better if I threw more money at it.
For the last few years, my priority has been obtaining records. The system is sufficiently "good" that I’d rather have more, different, and interesting music to listen to than constantly upgrade gear.

Not constantly, just to Austin Acoustic system.

Took the plunge and had a set of Cornscala "D's" built.
These speakers do everything I want from a speaker.
For the price they are fantastic, ugly as sin yes, but appearance is of no concern to me.  They out perform my mates Tannoy Kingdoms Royal's hands down at a fraction of the price.
They are not horn sounding at all, in fact people cant believe they are horns.
Horns done right just sound so real and lifelike to me, like music should.

Interesting personal observation I have tried various SET amps on these speakers, they are super sensitive and easy to drive, and every one of the SET amps just did not rock my boat.  They realy sing and come alive on my Opera Consonance Cyber 800 6CA7 mono blocks  @ 78 W. Go figure.

That being said:
I have listened to other horn speakers Avantgarde  Uno, Duo and the Zero 1.
Driven by different electronics in different venues and I am afraid to say they tore my ears off.
Also had a pair of Martion Bulfrogs for a week on demo, same story, just to much wrong with them.
Had the opportunity of hearing Unison research Max 2's they sound very good, they use the same horn as the Cornscala "D" very similar, but they are slower than the Cornscalas and lack bass in comparison, and cost one hell of a lot more.

Have been fortunate enough to hear Kinoshita RM-7V Monitors (horns) in a recording studio, these gave me the audio experience of a life time, closest to the real thing I have yet heard.

Have been a dedicated Vandersteen fan for a long time and have had many other makes of speakers and they have all left me wanting.  
Bought a set of Klipsch KG4's and they plus a friends DIY horn build got me interested in horns. They gave my Vandy 2 Signatures a good run for the money only thing they lacked in comparison was the clarity of the Vandies. All that at the cost of a night out.
Horns done right just do it for me, done wrong they are awful I have to admit.
And there seem to be many done wrong out there.

Kosst  it's all a matter of mathematics. Thanks it in these terms. You have a speaker that is 100 db efficient.  The source music goes from 10 DB to 30DB.  You multiply the two numbers together to get your final levels.  You are going from 1000 to 3000. Now take the efficiency of the speaker and substitute in a figure of 80db efficiency.  The source music still goes from 10 to 30. Do your multiplication and you get 80 to 240.  In the second scenario spread is much smaller than the first scenario.  That represents the dynamic range.Obviously this is a huge oversimplification  as the decible scale is logarithmic, but I think it serves to illustrate what I'm talking about. Increasing the power of the amplifier which can bring you to the same peak  levels will not give you nearly the same range. People continue to confuse dynamic range with ability to play loud and they are two different things. 
 So if you call continuing to try to correct misinformation not taking no for an answer, I am guilty as charged. 
Kosst  about 5 to 10 years ago I used to think just like you. I thought all vintage stuff must have been massively superseded by today's offerings.  I believed the magazines with all their reviews and advertising drivel.   Then I met a few friends who were older than me and had been into Audio since they were in their teens. They'd collectively pretty much owned everything at some point or another,  The one guy had made a lot of money flipping gear just prior to the Internet and in the beginning years of the Internet.   At one of their houses I heard Vitavox horns with SET amplification.  That's basically gear who's technology predates  the stereo era.  Granted it was set up with a top-of-the-line clear Audio table and Goldfinger cartridge.  Upon hearing that I realized that the best today's mega dollar offerings can hope for is to approach equalling it. In fact all of today's mega dollar offerings I've ever heard did not even come close, but I'm giving it the benefit of the doubt because I haven't heard all of it.  
The other funny thing is that with all of their collective experience, none of these gentleman ever, ever, ever participate in forums anymore.   In fact the one gentleman was a leading expert in the electronics and telecommunications fields for 30 years.   He holds numerous patents in his name. He has scratch built his whole system and it too is better than any modern commercial offerings I've ever heard. When I asked why, they explained that because when they try to correct the miss information they basically get shouted down and treated like idiots. I totally see what they mean.