Seymour said he had feared "American-style anti-intellectual, violent intolerance would come here".
"Universities exist to promote robust debate, educate, and search for the truth. They do not exist to coddle students and protect them from views they might disagree with," he said.
In a statement, Massey University said it cancelled a booking made by a students' politics club. It referenced Brash as a former politician and Hobson's Pledge founder, as well as a supporter of controversial Canadian speakers Lauren Southern and Stefan Molyneux.
Brash is a member of the Free Speech Coalition, which was founded recently by a group of New Zealanders following a decision by Auckland Council to ban Southern and Molyneux from its venues. The coalition argued the move breached the principles of free speech.
Massey said in its statement that club members approached university management concerned about their ability to keep the event secure after becoming aware of social media posts suggesting the event could lead to violence.
"The university considered providing additional security for the event, but decided the risk of harm to students, staff and members of the public was too great, particularly at time of heightened tension over the issues around free speech and hate speech.
"Dr Brash was also a supporter of right-wing Canadian speakers Lauren Southern and Stefan Molyneux, who were due to address a public meeting in Auckland."
Thomas said she supported free speech on campus but totally opposed hate speech.
"In my opinion the views expressed by members of Hobson's Pledge come dangerously close to hate speech. They are certainly not conducive with the university' strategy of recognising the values of a Tiriti o Waitangi-led organisation."
"It is clear there is heightened sensitivity and passion at this time, following the protests both against and in support of Ms Southern and Mr Molyneux's right to be heard. Our ultimate responsibility is for the safety and wellbeing of students, staff and members of the public on our campuses and under those circumstances cancelling the booking is the right thing to do.
"The members of the Politics Club have acted responsibly in raising their concerns with the university and are free to meet Dr Brash at another venue if they wish," she said.
Brash said Thomas had no grounds to call him a supporter of Southern and Molyneux.
"Am I defending them? No. I am defending their right to speak."
Brash said what Thomas had done was "very, very serious".
"I understand David Seymour's call."
