cardi How about "I don't believe in gender, because of XYZ, but I understand and respect that many people do, can we discuss that"? It's not actually that hard.
I am also surprised than in seminars you regularly didn't agree. Were all your seminars/modules compulsory? We, for the most part, choose our modules so largely the people choosing the modules are fairly similar, then everyone is split up into smaller groups. So you might get a group that mostly agrees, and a group that vehemently doesn't, I may have been fortunate to be in groups that mostly agree. Again, we don't agree on everything, but on the big stuff we did, and we've had feminism discussions where people did not ID as feminist at all (mostly because they viewed feminism in a fairly derogatory way) the people who did ID as feminist mostly shared the 'sort' of feminism they ascribed to.
Our seminar leaders, especially one, might not have particularly liked that we all agreed, or that we sometimes just made jokes about "TERFs" or less inclusive theories. But unless someone complained, they let you have open discussions like that. When, by a lot of people, this kind of thinking is viewed to be just as bad as racism or homophobia, it's clear people don't feel the need to respect those views or give them as much 'space' as other ways of thinking. That might be wrong, but it is what it is.
Maid a person can express themselves however they wish, if they are happy with the potential consequences of that expression. I wouldn't want to be judged, or to upset someone, so I'd just not give a reason.