Founder of the Iona Institute David Quinn has reiterated calls for Friday's marriage equality referendum to be rejected.
He cited an example from New Zealand, where he said two men got married "as a joke" after same-sex couples were given the right in that country.
He also believes two people of the same sex might get married simply to enjoy tax breaks, if the Yes vote wins - and that would change the definition of marriage.
Mr Quinn re-stated concerns that the nature of marriage would be changed if the Yes vote wins.
"If a man and a woman marry, it is always considered to be the sexual union of a man and a woman. If the marriage was never consummated, it can be dissolved," he said.
"There is now no pretence that consummation needs to take place if (the referendum is passed), so the whole nature of marriage changes.
"Marriage (would no longer be) the sexual union between any two people. It doesn’t have to be, and it doesn’t have to pretend to be."