The Christian-run bakery was found to be discriminatory in an appeal
A British human rights campaigner says people should be able to discriminate against ideas they do not agree with.
Peter Tatchell was speaking after a bakery in Northern Ireland lost an appeal over its refusal to make a cake for a gay rights group.
Ashers Bakery in Belfast refused to bake the cake with a pro-gay marriage slogan on it in 2014 - and Northern Ireland's publicly funded Equality Commission brought a civil action.
It alleged the bakery breached its statutory duty not to discriminate on the grounds of sexual orientation.
The Court of Appeal in Belfast upheld a finding that the shop unfairly discriminated against customers by refusing to bake the cake.
But Peter Tatchell told the Pat Kenny Show here on Newstalk this potentially sets a dangerous precedent.
"I disagree with them, but in a free and open society I think it's wrong that the appeal court to suggest that they should be effectively compelled by law to put a message on a cake (to) support gay marriage, when they themselves disagree with it".
"What's dangerous about this ruling...is that it implies that a gay baker could be forced by law to decorate cakes with anti-gay messages.
"It could also mean that other services providers - printers, t-shirt makers and so - they could be required to print sexist or xenophobic messages".
"In a free society of course serious hate crime should be unlawful; but merely expressing an opinion, such as opposition to gay marriage - even though I disagree with it - that's what freedom is about".