The fact that no one can contact anyone else (off the forum) may be an acceptable retort to those questioning the permissibility of non-essential online cross-gender communications. Nevertheless, the question is a valid one and I don’t understand the retort that if its a problem then YOU stay away and let everyone else be. That solution is good for the person but, if the problem is a valid one, does not alleviate the issue with the masses engaging in such conduct. And concern for everyone else is, surely, something we should all be concerned with.
Also, the retort that no one knows with certainty anyone elses gender is also true to a point. But in truth most posters make reasonably obvious their gender (as someone else pointed out above.)