What do you think about women writing M/M romance?
It's an open genre, and I don't think gender has anything to play with the strength or 'quality' of a story. I do get the notion of 'authenticity' though - as a queer teen I sought out books by gay men in order to, I guess, learn from the feet of those who had gone before me. But those weren't romances, really. Yet I also devoured Anne Rice's books and swooned over the tortured love of Louis and Lestat.
What I do think, however, is that when you're writing about a minority, you must show respect for them and be careful not to misappropriate. Allies must have a care not to become the spokespeople, and sometimes I think that gets shafted in the MM genre, when any time an LGBTQ person has a criticism to make they often get shouted down. It can be very discouraging and disheartening.
So a longwinded response to a very complex question - ANYONE can, and should, write MM - but please remember you're writing about a disenfranchised minority and not make the characters cardboard fetishes.
And also, I'm just one voice. You could find any other LGBTQ person writing in the genre who would very possibly think I'm being an opinionated arsehole ;)