I think it is reasonable to question what people mean by "can't discuss". As mentioned in the article people can discuss anything, but certain things are met with some pushback which makes discussing them hard or unpleasant.

I would say, if you hold one of these "taboo" opinions there is a reasonable amount of responsibility on you for how you open a discussion on them. If you do want to discuss them you need to try and raise them in a way which shows you are genuinely interested in discussion, including possibly changing your own opinion and trying to get a better understanding of others opinions without necessarily judging them. Rather than coming from a fixed position and trying to convert people, which in my experience rarely works.

If you hold one of more of these taboo opinions and think I am being rude, suggesting you don't discuss properly it that those you discuss with are all perfect reasonable beings that is not the case. But in my experience it is not common for people to open a discussion honestly looking to assess their own opinions as well as those they are discussing with. If you aren't open to change your mind, why should anyone be open to change theirs? If you are already doing that, then good for you! Hopefully some minds will get changed and we can all move forward with a more honest understanding of the world.