In my experience, the 'obnoxious and terrible people' tend not to be the casuals, nor the actual hardcore people going for world first, but the "hardcore" people who are in heroic modes. You know, the type that makes it clear that, because they're 3/8 H DS, that they're better than you (as they AFK in LFR and need on gear for vendor in 5-mans because only a scrub would actually need 378 gear this late into the patch.)

I disagree. I've seen awful people from each slice of the pie at about equal the rate. The only difference is, obnoxious people who have progressed through Heroic Mode have the gear to back up their talk (which doesn't make how they're acting right at all, by the way), vs. terrible obnoxious people in blues with wrong specs and pulling 5k dps and acting like their gods. It's much easier to tolerate and ignore douche bags with bad gear; You just laugh at them in your head. So it's not that there are "more" terrible people that come from Heroic Raiding, it's just that their harder to deal with because, dammit, they've seen and done more than I have (again, not that this justifies their attitude).

Purely anecdotal, but I'd say it's about 10% of all WoW demographics (casuals, hardcore, etc) that are simply intolerable people. Hence why I said that that more accessible you make the game, by a simple and elementary numbers standpoint, you're inviting a higher number of terrible people in. Which is where Blizzard's delicate balance of keeping the game's subscription's number high enough while still giving high-end raiding weight and value comes into play.

And now we're back to why Heroic Modes shouldn't be nerfed.