The ICC has accepted the Australians refusal to tour Zimbabwe. This is because, unlike the cowardly position the UK government took in 2004, voicing oppostion but not banning them from going, this is viewed as a government policy and therefore not the problem of the cricketers.
My point of view - given that some of the best Zimbabwean cricketers of the last few years aren't able to play for the team, politics has already clearly interfered. The anti-democratic policies of Mugabe mean that it is acceptable to refuse to give the regime any credibility by visiting. But governments must say this, not the cricket authorities.
I am no fan whatsoever of Australia's John Howard, but at least he took the responsibility for making a political decision. Which, after all, is what politicians are there for.