This is the whole point, the ACL doesn't represent society, it represents a small segment of society. Yes 61.4% of respondents identified as Christian, but not all Christian's are alike and the ACL has a particularly conservative approach to Christianity (note there is a difference in respondents vs people, which is why you need to accurately describe your religious beliefs). Yes the ACL has the right to have its views heard. Yes the ACL has the right to be free to practice their beliefs. No, they don't have the right to have "Christian principles and ethics accepted and influencing the way we are governed". Having one religious belief used as governing principles naturally isolates other religious beliefs. This is not democracy, it is the politics of exclusion. Hence no gay marriage, even though the majority of people support the notion (estimated to be just over 60%).
But why do we have the situation where such issues as gay marriage can be disproportionately influenced by Christian activists?
No, because modern politics in Australia is played on the margins. There are rusted on Liberal and Labour supporters that politicians can count on, it's the swinging voter that they chase and pander to. Conservative Christians are one such group. They had a huge influence on the 2007 election, with large swings to Labour from Baptist and Pentecostal voters and large swings away from Labour in the 2010 election. But they are relatively small numbers so how could they have such influence? Because there were large enough numbers in marginal seats in Queensland and NSW to have an effect.
The joke about the watch and the lion doesn't apply here, because there is the equivalent of the lion. Large numbers of people want change on specific issues e.g. gay marriage (effectively the lion). But it is the Christian activists (the watch) who are having a disproportionate influence on policy. If there were not large groups of people looking for change then your analogy would hold.
Only a secular society allows for all people of all faiths (including no faith) to freely practice their beliefs.