Pietersen has been among England's most conspicuous failures on their tour of Australia, repeatedly getting himself out because of poor shot selection.
Former England opener Boycott places the blame in part on the England management, including coach Andy Flower, for not curbing his more flamboyant on-field excesses sooner.
But now believes the negative effect on the England's less experienced players means they can no longer afford to have him in the team.
He told the Daily Telegraph: "How do you tell inexperienced players such as Carberry and Root that you have to sell your wicket dearly and work through difficult periods in a match, but then Pietersen plays like he does? He has given his wicket away four times out of six. Each time they set a trap for him and he falls for it. He is a mug and the Aussies are laughing at him. They think he is a sucker.
"Senior players should always give a lead to the juniors, but with Pietersen it is all about self. He is going to do whatever he wants, play the way he feels irrespective of the state of the match or what is best for England.
"I do not agree that you have to let him play the way he wants. When the best player in the team makes stupid mistakes just think what that does to the morale of the rest of the players. KP is in his own world."
He continued: "It is also a failure of management as much as KP's fault. Andy Flower has allowed him to play any way he wants because he can win matches.
"Every mother knows that no matter how much she loves her child she has to set boundaries. The child has to know if you cross the boundary some privileges will be taken away until you grasp right and wrong.
"Andy should have told him long ago it is not on. But obviously he has let him do what he wants, so he keeps making the same silly mistakes. I actually think KP is too long in the tooth to change now...If I was Andy Flower I would be saying either he goes or I go."