England have delayed a decision on whether to go ahead with the trip until after a March meeting with world cricket's governing body, but the British Government has strongly advised the England and Wales Cricket Board (ECB) to call off the tour in protest at the policies of Zimbabwe President Robert Mugabe.
The tour is planned for October this year, despite England boycotting a World Cup match in Harare last year.
Stewart told ITV News on Monday, "In my opinion, unless things have improved from 12 months ago then I don't think the tour can go ahead - so no, I don't think the tour should go ahead."
He added, "We are all about playing cricket and it's all about entertaining people and going out to Zimbabwe and doing the job, but is one game of cricket or a series of games of cricket more valuable than someone's life?
"I think you look at each case individually and I personally think the tour won't go ahead.
"I think that is very sad because I've been to Zimbabwe and I've played cricket in Zimbabwe and it's a nice country."
Stewart, who was part of the England squad who forced the issue with the ECB over the World Cup match at the last minute, praised the way the domestic game's ruling body has handled the situation.
"The good thing is the ECB are giving it a good nine months - they should be patted on the back for that."
Eng to decide after a meeting with ICC