Absolutely, and it's much easier to open your mind if you feel safe that you won't be punished and/or ridiculed for your ideas.

Errm, how will you open your mind, if you are able to discuss with others, to read challenging ideas, to take on-board another point of view, when you are hermetically sealed in a "safe space"? Surely they are unsafe spaces, as they close off the world, fostering very singular view points?

Safe doesn't mean sealed. It just means safe. Let's say you want to learn to fight. Wouldn't you rather do it by going to a professionally run 'safe' MMA gym where you can get guidance, learn from your mistakes and try different things safe in the knowledge that no one is going to cave your skull in just because you can't yet defend yourself. Surely that 'safe' environment is a much better environment to learn in than just going to 'unsafe' biker bars and picking fights with random people. I'd even wager that you'll learn more and faster in the safe environment than the unsafe environment.

Easier than if you're forbidden from opening your mind at all ? Safe spaces are about preventing people from saying what they think. That's their purpose.

I see it more like setting some common ground rules. If you want to rugby tackle people you won't be welcome to basketball practice. Doesn't mean you're being prevented from rugby tackling people, just that everyone would be happier if you went to rugby practice instead.