Only really had the time to post about this now and gotta say I don't really buy Maro's argument for it and at the same time I sort of do.
Basically, the issue is that card types have always been seen as kinda "metaphysical" to the game. Card types are "important", constitutionally important to the structure of how the game plays, differently from, say, supertypes or creature types which are generally very minor markers whose purpose is, most of the time, to serve as markers for in-game card effects. Each card type basically does a thing that no other type does; lands are played directly from hand to the board for no mana, creatures attack and block, artifacts and enchantments don't, instant and sorceries are one-shot effects, planeswalkers can be attacked.
Each of those are fundamentally different in the way they play, and to write out what they do would increase complexity enormously. I mean, you technically could wipe out the creature card type and write
Eager Cadet this way:
Eager CadetEnchantment -- Soldier
Creature 1/1
(This card has power 1 and toughness 1. Any time this card's toughness is 0 or less, or it has received damage equal to its toughness, destroy it. During your turn, tap this creature to attack an opponent or a planeswalker you control. If untapped, this card can block cards attacking you.) Card types do, then, what keywords do but raised to the eleventh power: they consolidate a lot of information into one nice, compact mental box. And, due to being the building blocks of the game, this rather complex set of information is assimilated all at once at the beginning; you don't learn Magic then you go learn card types, learning Magic
is learning the card types.
That is why, I think, something being a card type is generally seen as a "big deal" (as far as the obscure theme of Magic design discussion is concerned anyway). People had issues assimilating, for example, that tribal was a card type instead of a supertype because tribal doesn't do anything of the above. It is just a marker that lets noncreature cards have creature types, but it doesn't
play any different than a non-tribal card would (outside of cards that play off the marker, I mean).
This system was never perfect, of course, the main issue being instant and sorceries and artifacts and enchantments. Instant and sorceries fill the same role - one-shot effects -, but at least the timing restriction makes them play slightly different. Artifacts and enchantments are much more severe. They are basically the same card type, all distinctions between them are artificial: the colorlessness, the tapping, Auras and Equipment etc.
But those distinctions were pretty much the compromise found to force artifacts and enchanments to be distinct. They are Magic saying "yeah, they are kind of the same thing, so how do we make them not be and give each their niche?" So they made artifacts generally:
(1) Be colorless;
(2) Be able to tap;
(3) Be able to be creatures;
(4) Be able to be Equipment;
(5) Be able to be Vehicles.
And 99% of Magic's cards, an artifact has had at least one of those traits. I think Alara had a few ones that weren't, there are Eldrazi, and Theros had enchantment creatures, but all those were exceptional due to thematic demands instead of an expression of a broad design philosophy.
And then comes Glass Casket and it has none of the above. It is basically Silkwrap, an enchantment, except it has an artifact frame. Maro says it is fine, essentially, due to:
(1) Flavor;
(2) Effect is white so the card needs to be white;
(3) The effect is something artifacts can do.
Consider this card:
Pot of GreedArtifact
When Pot of Greed enters the battlefield, draw two cards.
Is this card acceptable? It is basically a sorcery, except it plays off some artifact synergies and dodges some counterspells. It is flavorful -- everyone knows what Pot of Greed does. And the effect is certainly blue. But I think everyone would see this as weird almost in an Uncanny Valley way -- outside of specific themes, artifacts and enchantments aren't
supposed to do one-shot effects and then be there on the board forever doing nothing. Rules-wise, they
can do it, certainly; that just isn't what people
expect them to do. And even considering people's expectations of artifacts have been relaxed to allow for colored ones, people still sorta expect artifacts to be at least one of the following:
(1) Be colorless;
(2) Be able to tap;
(3) Be able to be creatures;
(4) Be able to be Equipment;
(5) Be able to be Vehicles.
Maro's arguments miss the point of why people feel weird about Glass Casket. It isn't about the presence of something, but the
absence; artifacts were expected to have a few things and Glass Casket doesn't have them. If Glass Casket had "
,
: You gain 1 life" added, nobody would bat an eye.
But the thing is, in last analysis, does it
matter? I mean, I just wrote this really long post discussing why some pieces of cardboard have "Artifact" written on them instead of "Enchantment", but what is even the point in writing this. Glass Casket is just one card, after all. And even if it weren't, so what? You'd have some slight bump in complexity, as the artifacts/enchantments split would be slightly harder to grok, but gameplay would be mostly unaffected outside of maybe making red slightly better at removing problem permanents, and black's newfound enchantment removal slightly worse. Artifacts and enchantments are basically becoming tribes of sorts. But gameplay wouldn't be changed otherwise in any substantial way. So I guess this is less about Glass Casket being good or bad and more about understanding why some people got weirded out about it. It really messes with the "mechanical aesthetic" Mel cares about.
tl,dr The whole Glass Casket mini-controversy is more of an expectations question regarding what artifacts are expected to do.