The 27-year-old was charged with 'successful deception of a match official' by the governing body for his perceived dive to win a penalty in the Toffees' 2-2 draw with Crystal Palace.
Unsworth feels that Niasse has been harshly judged by the three-man panel looking over the incident, however, and claims that the FA has set a "dangerous precedent".
"He was shocked and I was shocked. He doesn't tell lies and he wouldn't go down without reason," he told reporters. "He wants to score goals. Contact or slight contact, it doesn't matter. We're all bitterly disappointed.
"We will have to accept the outcome. I think it's a great rule but I don't think it changes my stance. Contact is contact and my view won't change on that. Anywhere on the pitch it's a foul.
"I think these people will be very busy if that's going to be the case. You will have to look into every foul across the board. We don't want contact taken out the game.
"I am all for protecting players but we do have to have experts who know what a foul is and those who don't know the game it's a dangerous precedent that could be set if decisions go against you that are debatable."
Niasse, who has five Premier League goals in seven outings this term, is the first Premier League player to be punished under the new Football Association law brought in at the start of the campaign.