No idea how you can draw a comparison between Artest and Stephenson. Artest was getting T'd up like crazy and thrown out of games and was a constant issue for the NBA. So far Stephenson's biggest "issue" is that Evan Turner didn't like him and he blew in Lebron's ear or snuck into a Heat huddle. That's more the level of if the guy isn't on your team he's a clown but if he's on your team he's loved (see Noah, Joakim. Pierzynski, AJ. et all) Best I can tell Stephenson hasn't had any real issues in close to 5 years.
Stephenson isn't a calm influence but I don't see the Artest comparison. Even the was Artest was getting T'd up back then makes Stephenson look like a choir boy.
Stephenson's instability doesn't go back just to this season. There's been a clear history of it. He left his initial HS because he didn't win MVP of the youth league that summer. He was cut from USA Men's Basketball Under-18 team because he was causing problems. He had a sexual assault charge his senior year that cost him several top scholarships, including Kansas and Maryland. He was in some documentary that almost made him ineligible his freshman year at Cincinnati. He was benched for a good portion of his rookie season in the NBA for being a disruption. He even blew in Lebron's ear the playoffs BEFORE last year too.
Then this past season, after an all-star snub, he resorted to selfish play and clashed with teammates (not just Evan Turner btw) which helped nearly derail the Pacers' season. Stealing of rebounds, ball hogging, avoiding timeout huddles, never sitting on the bench, trash talking on and off the court, and the egregious flopping and unpredictable play were all on display this season. While I'll admit he has that "irritant" quality, I find it easy to dislike this guy even if he's on my team. He's very much like Artest in this way.
Hopefully this kid can screw his head on straight but he's by no means just a typical "clown" like Noah or AJ. Both of those guys may be considered clowns by others but they would lay their LIVES down for their team, and Lance doesn't appear to have this quality yet.