The Toowoomba doctor found his medical centre vandalised with the word “Bigot” painted in red spray paint on the side of his office, along with his surname in black paint.
An encircled letter A – a common symbol for anarchists – was also left on the building.
Dr van Gend is president of the Australian Marriage Forum which recently attracted controversy when it raised $20,000 to pay for two ads on opposing marriage equality during the Mardi Gras.
SBS rejected the ads, but they were screened in prime time on Channels 7 and 9 instead.
Toowoomba Police confirmed they were investigating the graffiti attack.
“My point in noting it is not because it worries me particularly, I’m used to this,” Dr van Gend told the Brisbane Times.
“It’s a symbol of the whole intimidation and demonisation of one side, and one side only, of this debate, and it must stop.”
“I get so much of this, but usually it’s anonymous trolls online,” he said.
“Internet trolling is one thing, but this is malicious damage. I don’t own the building. It’s someone else’s property they’ve vandalised.”
Dr Van Gend says his name plaque on the building has previously been defaced and his staff have received abusive phone calls.
Dr Van Gend believes the same-sex marriage debate has become “unhealthy”.
“Anyone who stands up for the law of the land, for saying that marriage is between a man and a woman… is attacked, not argued with,” he said.
“And that’s what happened [the vandalism to his surgery] yesterday”.
Dr Van Gend says he is not opposed to debating the issue, but he is opposed to threats and abuse.
He says it would be beneficial for both sides of the argument if people “assume goodwill on each other’s side, argue a case, and then vote.”
He says the vandalism attack is “a sad comment on the approach of the pro gay marriage people to any of us who dare raise our little heads and say ‘keep marriage the way it’s always been’.”
“The mother and father unit is so strong, but people are frightened to put their head up, because they won’t only get their surgery defaced by vandals, but they’re going to be treated like they are some sort of moral pariah.”
Apart from a stance against same-sex marriage, same-sex adoption and same-sex surrogacy, the Australian Marriage Forum also argues against the idea that homosexuals are “born that way” and disapproves of the “normalisation” of same-sex relationships being introduced into school education.