The Bishop of Honolulu has warned against attempts to legalise equal marriage in Hawaii and says Catholics in the US state must pray to defeat it.

In an open letter, Bishop Larry Silva said: “If same-sex marriage becomes the law of the land, its implications will go far beyond the relationship of this or that couple. There will be long term and definitive changes in our entire culture. If same-sex marriage becomes the law, it will become ‘normal’ or the norm for our land.

“If one may marry without discriminating whether the partner is of the same sex or the opposite sex, then such ‘non-discrimination’ will become the norm in other areas, too. Our school textbooks will have to portray sexual attraction as normal, no matter to whom one is attracted. When schools have dances, boys will have the choice of inviting a girl on a date or another boy on a date. Our youth, whose sexual identity is formed over time, will be forced to decide prematurely if they are heterosexual or homosexual, thus curtailing normal sexual maturation, with all its stumblings and challenges.”

Suggesting equal marriage could lead to polygamy, Bishop Silva added: “If same-sex couples are given the legal right to marry under the pretence that discrimination that excludes them from marriage is unjust, why would people who prefer several spouses at the same time not be afforded the same right? Why would we taxpayers be exempt from paying for marital benefits for all those spouses? Why would there be discrimination against those who decide to marry their mother or father, brother or sister, so that they can gain spousal benefits for them?

“Once we give in to the false notion that same-sex couples have a right to marry, how can we reasonably deny the same ‘right’ to anyone who chooses to enter a ‘marriage’ with a close relative, a minor (with consent)? If same-sex marriage becomes ‘norm’-alized, would parents be considered bigoted if they raised their daughters to be attracted to boys and their sons to be attracted to girls? Or must parents now be completely neutral in steering their children toward the choice of a mate?”

The Bishop also claimed marriage equality in Hawaii would lead to greater suicide among young people.

“Children will be the greatest casualties, in that they will be deprived of being raised in a loving home by a mother and a father who loves them and whose love cooperated with God’s plan in creating them. When children are deprived of such a home, there will be more poverty, more social ills, more juvenile suicides, and more problems than we can imagine.”

Civil unions have been legal in Hawaii since 2011. Campaigners hope lawmakers will be able to debate equal marriage in the state legislature later this autumn.