The head of the Equal Opportunities Commission, the city's anti-discrimination watchdog, also expressed concerns that politics was mixing with religious beliefs.

The Hong Kong Catholic Diocese is known for being vocal on issues like democracy and social justice. Its position on gay marriage was reiterated in a pastoral letter from Cardinal John Tong Hon, who said the city's core values on marriage and family were being challenged by sexual liberation and gay rights movements.

Watch: Hong Kong LGBT protesters say city lags behind in gay rights

The remarks raised question about whether the local church was taking a harsher line than Pope Francis, who has struck a more conciliatory tone on gay issues.

The reference to drug abuse by auxiliary Bishop Michael Yeung Ming-cheung was probably just an example to illustrate the church's position on homosexuality. Abusing drugs was wrong, he said, but the church still cared about drug addicts. But the church's position could be misunderstood as denigrating homosexuals by linking them to drug abusers.

The cardinal's appeal to followers to take into account candidates' position on gay rights is unprecedented in Hong Kong. Like other social groups, the church is entitled to defend its beliefs. But it should be noted that most district council aspirants do not make clear their stance on gay rights.

The issue arguably becomes even less relevant as the district councils have no power to legislate. Whether a candidate's position on gay issues should be taken into account is ultimately for voters to decide.