More than a few people on HLP play, and aside from Hades and maybe 0rph3u5 none of us could be considered morons.
Save hackers like Astronomiya and I, but not morons.
We do not cheat when playing with people who do not cheat, so don't worry about me showing up with a maxed-level Hunter and sniping everything from a mile away with a perfectly-steady Keen Sniper Rifle of Flame +5. Astronomiya, Commander Zane, Scotty, Ravenholme, BritishShivans, Hades, 0rph3u5, Valathil, and I all have BL1, but that's just the people who have offered to co-op with me. Our availability and willingness to play may vary by region and level of give-a-damn.
And yes, co-op is great. SP is about as average as single-player Diablo, but like Diablo MP is a blast as you and up to three friends murder your way across the planet.