Having opinions
...is not the same as voicing them. You can have opinions on anything and everything, but once you voice an opinion you have an obligation to listen to criticism of it. I'd actually go a step further and say you have an obligation to reconsider your opinion in the face of opposing evidence.
To be truly open-minded, it isn't enough to be open to listening to dissenting or contrary opinions. Anyone can do that. You must be willing to go a step further: accept that the dissenting opinion is exactly as valid as yours. Accept the fact that there exists a perspective where your opinion is wrong, and that you must often be willing to make the jump to the other perspective. But you can't do any of this unless every time you voice an opinion, you are willing to accept that it might be wrong.
This also means that every time you run into someone else's opinion, your default mode is to accept and validate them. Of course,this doesn't mean you have to agree with every opinion you run into. There's a difference between acknowledging someone's reality and living in it.
I have lost count of the number of times I've heard people – at work, and outside – talk about creating safe spaces. More often than not, the conversation is about accepting me for who I am, and my feelings not being hurt. I believe the conversation should happen the other way around. To truly create a safe space as a refuge for difficult conversations, I must be willing to accommodate opinions and perspectives completely alien to my own, while making people who hold them feel comfortable having and expressing them.
A true safe space requires more effort from the listeners and receivers, than the opposite. It mandates an open mind.