yay or nay?
Nay.
The vast majority of defensive stats in LoL target a solid ~50% of the damage sources avalible in LoL. HP targets everything besides %HP damage.
And health, armor, %attack speed slows, Ninja Tabi's reduction, and Thornmail all target the vast majority of auto-attack stats: AD, AS, and Crit are targeted equally by all of them. Armor penetration and life steal by a solid 50% of those as well.
Critical reduction? Litterally only targets critical strike chance.
Which is a serious problem when considering the prevalence of critical strike chance in LoL: not very.
Out of tanks, fighters, assassins, marksman, mages, and supports - only marksman are likely to get critical strike chance more often than not. A few fighters and assassins are designed to persue critical strike chance, but you're mostly looking at Tri-Force's 15% as being the only reliable amount outside of marksman. And reducing 15% crit chance by 100% to make 115 DPS 100? That's only 13% damage reduction. Which is like, 300 HP when you're level 18. That only works against crit.
Also on this - Tryndamere and Ashe are the only 2 champions, far as I'm aware, that actually have critical strike chance built into their kits. Everyone else starts with 0 - which means if you rush this crit-reducing item? Literally no benefit at all. Get it for your second major item? Marksman might not even have 25% crit chance, which means, again, you'd need impossibly high values for very minimal benefits.
And end game with 3 major items, and a Yasou - you're looking at critical strike damage being about ~20% of the damage you take from an enemy team (where it's 0% at the beginning). AD skills like Peacemaker, Mystic Shot, and Last Breath don't actually crit, and make up close to 50% of the damage of crit-happy marksman and assassins.
The 20% AS slow on Frozen Heart at least hits about 25% of an enemy team's damage at all points in the game, rather than just end game.
Anyways - If such an item was actually good enough to be picked up regularly against that 0~20% crit damage - it would shut down critical strikes reall, really hard to realistically be a viable choice.
And with that, also important to keep in mind Crit is an optional stat marksman and assassins don't even need to get in the first place.
If an anti-crit item was solid enough to be a regular buy in the harsh enviornments I listed, then 
is still a viable build with a heavy focus in marksman skill damage, and a 100% DPS increase in the form of AoE.
TLDR:
Crit is such a specific stat to target any anti-crit item would be awful.
In the off-chance it's so OP it's not awful, it would shift the meta so players simply wouldn't buy crit. And then it would be awful (again).
already works as a kind of anti-crit item by making crits deal tons more damage against the attacker. I wouldn't really want a dedicated crit mitigation item in the game, mainly because it's only useful against one class, but also because crit itself is a fiddly enough system, and doesn't need any more additional variables.