The Tavern

Cursed items, poisonous potions, scrolls with harmful magic. All that stuff came from other roguelikes - like NetHack or ADOM. But the thing is - Dungeon Crawl is different. It is vastly different. The main point of ADOM or, especially, NetHack is that it is more game itself which tries to kill you, not monsters. In NetHack, it is not unusual, to equip a cursed loadstone, and then, start to wildly read scrolls you found, hoping to uncurse and drop that stone, and as a result get crushed by a boulder. Moreover - most of the stuff which harms you in those other roguelikes can be useful. For example, if you drink unedentified potion of rust removal, you will get severly posioned. But when identified, it is actually a very useful tool. Potions of poison can be thrown at enemies or used to coat your weapon. Above mentioned scroll can be used to isolate enemies from you. And so on. Dungeon Crawl is not about that complex item or potion mechanic. It's about strategy. It warns you when you try to step in lava, or in range of Okhlob Plant. Prevents you to do stupid things. But, in Dungeon Crawl monster behaviour is wastly improved compared to other roguelikes. They work as a team. Some share damage with allies, some buff their allies or heal them, some has interesting abilites to lock you in a vault, so you can get gangbanged more easily and so on.

I written that paragraph to ultimately conclude - DCSS do not need stuff like potions of degeneration, scrolls of random uselessness, amulets of inacurracy, cursed -n equipment and so on. This stuff can mostly mildly annoy you at early game, and otherwise completely redundant. It's monsters who devastate you there, not items. It is not NetHack. So, that stuff should either be reworked to be not utterly useless (like scrolls of noise, which sometimes can be used to attract attention to the place you want to fight monsters, or to break mesmerisation), or completely removed.

The mesmerisation interaction was removed over a year ago.

regarding your examples ...

- imho degeneration can stay as long as the identification minigame stays. it is "harmful only", but its effect is rather minor and it can add to the early game.
- I wouldn't say that random uselessness is harmful at all. It is at most one lost turn in a battle in a game of xxxxx thousand turns at least. It adds a bit fluff to a game that lost too much of it.
- Inaccuracy could be removed as a non-artifact amulet or not, it wouldn't change much since there are several other amulet base types that you might not want so you're probably id'ing them anyway. I really like inaccuracy (or other usually harmful base types on jewellery or armour) if they come with otherwise desirable attributes, this can lead to interesting decisions once in a while.
- curses, well, ash, I wouldn't like to lose her. But they don't fit into the game well, I agree.

I like it when items can be desirable in some cases, but useless or harmful in other. DCSS does this sometimes quite well (lignification, noise, immolation, desirable artifacts with undesirable base type), but I think it's quite hard to design those. Overall I think that DCSS is not too overloaded with useless stuff, and those should rather be reworked than simply removed.

Curses can be removed while preserving Ashenzari, they'd just become an Ash-exclusive feature. Cursing and uncursing items would just have to use something other than Remove Curse scrolls, which would not exist.

Scroll of noise is pretty meh as a harmful item, too.

Scroll of noise still has it uses. It's particularly useful for waking up Zot:5 so that all the monsters teleport out, thus making the lungs much much easier.

come on man

First time I played Crawl I spent an hour trying to figure out how to throw Potions of Degeneration, Lignification, Mutation (and I believe Potions of Poison were in the game?) at monsters after drinking one. I believe making it work would fix the OPs concerns about harmful-only stuff. (I also wielded Frenzy Needles to stab things, but not as relevant.)

Edit: If thrown potions were a thing, it would also open the door to many more interesting potions. Like potions of rust.

Isn't potion of rust = wand of acid?

Personally, I'm always OK with limiting the number of item types in the game, as long as it doesn't detract from the game. Somehow, I think that potion of degeneration has its place. Scroll of noise doesn't. Random uselessness also is unneeded. Removal of curses would require removing the ID game of equippables except amulets.