EDIT FOR CLARITY AT BOTTOM.
I don't like alternate difficulties of the same content to be part of a games progression, and I will explain why I feel this way.
I respect the opinion of those who do enjoy what I am about to describe, but I simply hate this form of progression and it bores greatly.
Let me use an example of one of the most recent games I've played: Diablo 3. (probably not the best example in hindsight)
I love Diablo 3. I beat normal, nightmare, and I'm working on hell, but I found myself drained of enthusiasm for the game a little ways into act 2 of nightmare; why is that? Mainly it's because it's the same game, except with different loot, more health on enemies, and more damage done by enemies. I was intrigued by elite mobs with abilities absent from normal mode, but that was all that really interested me.
Normal mode was the most fun for me because of the feeling of fresh content that I've never done before, but it was too easy and I had no option to make it harder on myself other than gimping myself through using lesser gear.
Another example of this is from WoW. I had fun doing raids the first time, doing it on any other difficulty after doing the easier mode felt boring and tired despite it being more challenging (I guess, it's still basically a competency/gear check that 9/24 other people must pass with you). Fights like Ragnaros Heroic pushed me to want to see it because of it adding another phase and lore ending.
Basically, I play content for the experience of the content, not to unlock a greater challenge of the same content through gear or completion requirement or otherwise.
I like difficult like most console games: Select desired difficult at the start of the game. A god example of this, however not a difficult game, is Kingdom Hearts.
In Kingdom Hearts, you have the choice before the game starts of 3 difficulties: Beginner, Standard, or Proud. Each encompass the entire game, you don't have to complete one before the other, and you get a secret ending easier inverse to the difficulty you selected as a reward/downside to the difficulty chosen.
I like this system of difficulty because in all 3 difficulties you're given the exact same skill sets, but have harsher or easier conditions to combat but it can be fresh and challenging for skilled players from the get go instead of having to slog through faceroll content to get to the content suitable for your skills.
I'm a firm believer of "If you can't complete the content, you don't deserve to see it" which is opposite of Blizzard's current philosophy. I'm not saying that because "I'm elitist and believe that only I, the elite, should get to see content," I rarely get to see end game in WoW. I don't believe a person is entitled to see the end of a game if they payed 60$ or are paying 15$ a month if they aren't good at the game. The player should rise to the challenge to see the content, the game should never lower itself, which is exactly what the first difficulty system does, but it also makes the harder difficulties less interesting because it feels like backtracking for those who actually wanted a challenge in the first place.
I'm starting to get off track I feel... (aka, TL;DR)
All I think I'm trying to get at is that:
I don't think easier difficulties of the same content should be forced upon the player, but should be an option.
Players should rise to the challenge of the game, the game shouldn't lower itself for the player.
I know this is a stupid rant, but I felt like I had to get this off of my chest somehow, and typing it into a thread was the best way I could think of.
EDIT: I'm not lashing out at any game. I'm not claiming to be elite, and I'm not saying that only the hardcore should beat a game. I'm just disagreeing with the progression method of requiring lower difficulties of the same content to be completed before higher ones.
The bit about "rising to the game's challenge, not the game lowering itself to the gamer" is just a little extra I felt I wanted to add, since it is the way I think games should be. If a player can't complete the lowest difficulty level, then the content shouldn't be nerfed to accommodate them, they should become better to accommodate the content. Humans have the capacity to learn from their errors, and learning from defeat in games is no different unless you have a mental dysfunction.