Obviously not guests in the formal sense, since the hosts are MNHQ, and we are all heir guests -- but guests in the sense that they are visiting the cultural territory of women, need to respect the mores there and ought really to be present insofar as they remain welcome.
I don't say that with any hostility, just with a desire to preserve a female space. I like men very much, most of the people I have learnt most from have been men, and for many years I had few women friends.
But I value just an element of separatism -- for women and for men. I have two sons, no daughters, and I am very conscious of ways in which society is challenging the legitimacy of some elements of maleness. Men need a sphere to celebrate maleness, women to celebrate femaleness, and all of us can share other spaces together.
Like it or not, mumsnet is a robustly and wonderfully female place. Just because that is what it is, it should be allowed to continue unashamedly as such.