Gonchi: Don't like the practice, won't support it. What's there not to understand?
In broad strokes this is how I feel, too. I don't agree with the approach and I don't agree with the reasoning that "makes it right" for them to use it. It's a practice to solicit new high-tier pedges by promising a different/special version of their game exclusively for (a subset of) backers (and ultimately of buyers of their game). From their perspective, it probably looks like a smart and justified practice (I suppose a good number of people would go for the "complete version" of the game, even if "complete" means having some extra pointless or game breaking items -someone in the comments already requested an option to disable the extra items in the special version).
From mine point of view, it sucks that what works essentially as a first day silly exclusive DLC addon (in the "best" case) or a different game version of limited-copies (in the worst case) is used to promote support for a crowd funding campaign. Where a pledge is not mainly put to buy the game (it's not supposed to be a preorder albeit most campaigns end up using all their tiers like that), but to support its team and their practices, to enable them release their (full and complete) game to the public.
Anyway, AstralWanderer, explains it quite better than I do probably.
Also, what AstralWanderer suggests (time limited extras) is a compromise that has been suggested before in most (all?) of such situations where this controversy arose. It still doesn't make the practice go away (which is a main issue for me), and in this case, it automatically creates the defence "but now we have to ask confirmation of all those who pledged higher than X", but I do like this game's design very much, so I would at least seriously re-think pledging should they promise something like that.
In any case, this discussion seems to be going the same path every time I've encountered it. The ones who don't mind (and sometimes the dev team too) are on the side of "why do you care, it's stupid extra stuff, the base game experience is completely unaltered" and the other "side" is of the mind "I don't support the release of slightly different versions of the same game one of which is offered exclusively to some, while excluding all others" .