While I concede the effort requirement (there are shitty people who really shouldn’t be parents), from experience of raising two children, it’s perfectly possible to train them to do and think how you want - it’s all a matter of starting young enough and staying consistent.
Once they get older, it gets trickier (outside influences such as peer pressure and the internet for example), but in most head canons, fluffies never get much beyond toddler level, plus you can legally use significantly harsher discipline methods than that for human children.
Pain and punishment applied appropriately is an excellent teacher, especially for those instances where they’re incapable of understanding higher reasoning or for when you need cultural indoctrination (e.g. the military).
Fluffies exist on a weird middle ground between animal and human, dumb enough that they can’t grasp complex concepts like human society but smart enough that their self-image is severely affected by this stuff.
I’m a little confused here. You’ve said that your alicorns have their self image severely by seeing themselves as a monster; so they do pass the mirror self recognition test?
While I agree that fluffies aren’t clever enough to understand higher concepts, basic elements of human culture should be easily understandable to them; in most headcanons, fluffies form feral herds with a clearly defined hierarchy, much like human society; do your fluffies not do that?
It sounds like your fluffies are less capable of training and socialisation than in most headcanons; can not more basic training be used for them? If dogs can be socialised and trained to perform specific tasks, then you should be able to train your fluffies. If they’re smarter than dogs, then step up the training complexity - as an example, USMC training is excellent at indoctrinating and training civilians of all intelligence levels into becoming a marine (the average highschooler will score a 50 on the AVSAB entry assessment, the minimum for a marine is 31).
These fluffies’ wings aren’t true wings and their horns aren’t true horns.
If removing the horn can cause infection, that also means there’s a blood supply attached, so are they flesh covered cartilage (like an ear), or a giant fleshy protrusion with its shape maintained by blood pressure (like a penis)?