That's actually because Crimson honestly shows how bad it is, unlike the Confection who is just as hard on your body as a disease. You could also get ill with what the Confection wants to offer you, but you could get just as ill with what the Crimson has to offer. The Confection could make you just as rotted and bloody (ulceres, tooth rot, infected digestive tube wounds, etc...).
I'm mostly supporting my idea because I'd like some more progression, bringing something else than Cyber and Crimson in a Cyber/Crimson world would create a new, more powerfull chimeric biome which would offer a totally new fight. I'm not really for having 5 alts for a "good" biome and another 7 for "bad" biomes. I don't know, but if I were new to Terraria and would reach Hardmode, and the guide/dryad warned me that bringing seeds of an otherworldly power (pearlstone, in our case) would result in a great imbalance, I'd definitely try that out. I find diversity just for diversity's sake rather bad, as I already mentioned above, so mixing chaos and order with goodness and badness and see what would happen would definitely be some interesting mechanic.
That's merely my point of view, rest assured that I don't expect my suggestions to be implemented in-game.
