I personally think four difficulties is excessive. I wish they just made LFR a smidge harder and kept it queueable and made that normal.
That said, in defense of LFR, I raided weekly fairly hardcore in vanilla/tbc before taking a break in wrath after a guild implosion. After that it was hard to get motivated to find a new raiding guild. I floated through wrath/cata and most of MOP until I discovered the LFR in late panda. There was huge novelty in the ease by which I could get a raid group going (unheard of for an early days player) and jump into doing something that was at least sort of like something I had liked so much. It was also exciting to go through the expansion's raids to get a glimpse of what had happened and what I'd missed (I resubbed sometime toward the end of the 14 month SoO drought). Getting that taste of raiding was just what I needed to get back into it and before I knew it I was doing flex raids and moving into heroic and eventually mythic Siege. This continued into WoD where I continued raiding at the heroic and eventually mythic level.
So basically, for all of its flaws, LFR can be a gateway or intro/prep for raiding. The hope is that it will leave the player wanting more challenges like that to move up the ladder, rather than simply being complacent with floating through the LFR model.