The "malus" is not on the gear, but related to your total corruption stat. At certain levels (0,20,40,60) you start to gain more of the debuffs in your list of possible procs. At 60, you seem to get a permanent debuff (The tooltips for the other effects say 1 proc per minute, this one does not), which is 60% damage taken and 60% less healing, which basically means if you go over 60 you're screwed unless you drastically over gear the raid, and even then I doubt it'll be manageable unless you can nuke the bosses in under a minute. Not to mention, this debuff scales up the higher you go, it's possible that with 100 corruption (which won't be hard to reach) you won't be healable. Yes, you can cleanse an item, but when you look at the string that gave us this info (Cleansing this item will REMOVE the following effects: ) you can see that is say effectS, meaning it removes multiple things, since the item has corruption and a bonus, it will likely remove both.
That being said, there is seemingly a way to reduce it and essences to add resistance, but since items seem to have ~20ish corruption it's likely we'll only get to equip 4-5 at a time because going over 60 corruption is just not supportable in a raid until super late.