England hooker Hartley, 28, caught Tigers centre Matt Smith with an elbow off the ball during his side's 23-19 Premiership win on Saturday.
"You won't change Dylan," said Mallinder. "Dylan plays to the edge.
"He's competitive, but you can think of a lot of players in the past who have been competitive and sometimes it's just not worked out for them."
He continued: "I thought it was probably a yellow card and didn't deserve a red.
"He should have kept his arms down. We're not saying what he did was right. What I am saying is that the opposition made it a lot easier.
"I think Smith went down pretty easily, which was disappointing."
Saints captain Hartley had admitted last year he was in the "last chance saloon" when it came to his England career, following a string of misdemeanours.
In 2007 he received a 26-week ban for for eye-gouging Wasps forwards James Haskell and Johnny O'Connor.
And in 2012 he received two separate suspensions, an eight-week ban for biting the finger of Stephen Ferris and a two-week ban for striking Ulster's Rory Best, before his red card for swearing at referee Wayne Barnes in last year's Premiership final cost him a place on the British & Irish Lions tour to Australia and 11 weeks of rugby.
"If you strike somebody in the face you're liable to get yourself in trouble," said Leicester director of rugby Richard Cockerill.
"You would have thought he might have learned a lesson by now."
Hartley, who has 61 caps, could face at least a two-week suspension for elbowing Smith, however a Rugby Football Union disciplinary panel could mete out anything from nine weeks on the hooker if they deem it to be a top-end offence, although this is unlikely as Smith was not injured in the incident.
England start their Six Nations campaign in seven weeks' time against Wales on 6 February.
Northampton boss Jim Mallinder admitted Dylan Hartley "plays to the edge" after his sending off against Leicester.