The point of raid lockouts is simply to keep raid farming from happening-- guilds could farm Gruul over and over again, or run into Serpentshrine, down Hydross, and just keep it up for the whole afternoon, picking up Epic after Epic. But as Alcaras points out, guilds already farm-- the 5mans (including Heroics) are already farmable, and no on is arguing that Heroic gear is too easy to get. Plus, things are getting pretty silly-- some groups are running three or four Karazhan groups weekly. How much more would they really run it if lockouts were removed?
Of course, eventually, Alcaras will get his wish. Blizzard has a habit of eventually tuning down and opening up the lower dungeons-- that's what happened in UBRS (originally a 15 man dungeon), and Scholomance (originally a 10 man dungeon). Sure, it likely won't happen anytime too soon, but eventually, Karazhan is going to be nerfed, and the lockdown removed. But I tend to agree with Alcaras, at least for the first few high end raids-- the only real consequence of opening up the lockdowns is that more players would get to experience raiding content more often, and in my mind, that's a good thing.
[ via Tobold ]