Malice or intent has absolutely nothing to do with it. If he doesn't take Vardy out, Vardy passes him and has a shot at an empty net. It's denying a clear goalscoring opportunity. It's one of the most straight forward red cards you're ever likely to see. Utterly baffling he wasn't sent off.
And the "double punishment" cop out some pundits trot out is BS too as it assumes the penalty is going to be scored. If it's not, then you can just as well argue Leicester have been denied what would've been an almost certain goal illegally with no proper punishment and Watford have been rewarded for stopping a likely goal illegally. You only have to remember Suarez stopping a certain goal with his hands in the 2010 World Cup against Ghana to show how if the penalty is missed then the illegal stopping of the goal is rewarded, as a penalty is not necessarily a fair compromise for illegally stopping a clear goakscoring opportunity and at least the red card atones for that somewhat.