The tour involves five one-day international matches.
Thorpe has retired from one-day internationals, but will join up with Michael Vaughan's squad for the five tests in South Africa starting in December.
He told UK newspaper The Mail On Sunday: "(The ECB) have allowed themselves to be bullied by the ICC (International Cricket Council) and they in turn have bullied the players psychologically with threats of what will happen to the game in this country if they don't tour."
In March, the ICC said any country refusing to fulfill their tour obligations for anything other than security reasons or governmental direction would face a minimum $2million fine and possible suspension.
Thorpe said players could not understand "a logic that says it was right to pull out of the World Cup match in Harare last year but wrong not to travel now".
Pace bowler Steve Harmison ruled himself out of the tour two months ago for political reasons and the ECB said at the time any player who made himself unavailable for reasons of personal conscience would not be penalised.
Skipper Vaughan, one of four senior players offered the chance to miss the trip on cricketing grounds, admitted last week he was not looking forward to the tour.
England forfeited a World Cup match in Zimbabwe last year after the players voiced concerns about security and the human rights record of President Robert Mugabe's administration.
