If Artest seriously injured or killed the guy it would be different (and he easily could have)--- apparently from the news stories, no one was injured too badly and only a handful needed any treatment.
The way to maintain that particular image is to kick your opponents' ass on the court, not in the stands. Doing the latter would create a brand-new image -- that of an out-of-control moron. .....and possibly a permanently out-of-work one.