Yes, they can. I personally don't even curse, by default, but I'm not offended to read the random swear, unless it is actively used to be an insult towards someone, which was not the case here.

I am interested in making sure people are allowed and expected to express themselves freely in this space, unless they break the "rule" I mention above.

Don't censor yourself. If there is need for a swear, use it. Just don't use swearing in place of proper speech.