>>/10787/
> A name I know... from long ago. Never read (or maybe I did but forgot, been so long) 
Well worth a read/reread. After a certain point I stopped, but all the early chapters are fantastic.
> I mean an attitude where dark and gray are only valid. and anything else is just for babies 
Oh, I see what you mean. I feel like they're maybe less outspoken these days too, especially since colourful Superhero films are more the norm now than gritty realism, but that attitude certainly still seems to make the rounds.
> I had a notion I would have to give up most "childish" things like that when I grew up at a certain age. 
I tried, but I couldn't bring myself to do it.
 >>/10788/
> Seems like a harmful spell could be a curse for all intents and purposes and that poison joke arguably is.
Part of the trouble is definition. In our world, people will say magic is real, then say that it's not supernatural powers at such, but the ability to manifest a particular reality in your life, or something to do with sleight of hand. In the same way, poison joke could be viewed as a sort of plant curse, but I imagine ponies define magic as using life energy with a particular intent. Mind you, the tree of harmony breaks those rules, seemingly have intentions behind what it does. As for harmful spells, I would suggest that the difference is probably something along the lines of how reversible curses are, or how long the spell lasts. A curse is presumed in a lot of cases to last for a long time - we see Twilight do things like give Spike a moustache and turn a frog into an orange-hybrid creature, but perhaps these effects are strictly temporary. We see an enchantment on those tickets I keep going back to, which makes me think that a curse within in-universe magic-logic would essentially be a harmful enchantment rather than a spell. Perhaps, then, living creatures are resistant to all forms of enchantment, but even then, you can have cursed objects. So perhaps Twilight is referring strictly to interpersonal curses, since evidently objects can be cursed. Another angle is she might mean curses in an even more specific sense, like Equestrian versions of the evil eye, walking under a ladder or breaking a mirror. Obviously they haven't done the latter two here, but perhaps what Twilight means is that Zecora doesn't have a horn with which to perform magic, and that curses are a crude superstition of non-unicorn magic. That makes some degree of sense, though again with the later Pinkie premonitions episode, I think we see suggestions that Twilight is in fact mistaken about the magical potential of non-unicorns. Well, obviously we meet lots and lots more magical creatures later in the show, but at this stage I mean. Perhaps things like Discord and Tirek have faded sufficiently from memory that the academic consensus is that unicorns and alicorns are the only creatures that can enact active rather than passive magic. Though all that sort of "forgotten knowledge" stuff does always beg the question of why Celestia has ALLOWED these things to be forgotten, even to her personal proteges - speaking of which, was Sunset her first? Or maybe Cadance? Or has Celestia been taking on personal students for centuries by this point? Way later in some of the EQG stuff we discover that Canterlot Library has a restricted section that Celestia has access to, so there is certainly some degree of classification or even censorship with Celestia's authority, but the rationale behind it (maybe preventing Cozy-Glow types) and the technicalities of how it's enforced aren't clear. 
> I should have a new one up myself this time soon though. 
Looking forward to it!