A frank, interesting and enlightening discussion. Mark is clearly an intelligent, educated and articulate man, leading a typically masculine and heterosexual life - but generally in skirts and heels. He is no male oil painting and could not easily pass as a woman, but (as he explained) he has no wish to be anything other than a 'person' wearing certain clothing of his choice, that happens to be feminine in style. If he influences or persuades other men to adopt a more fluid appearance, without sacrificing their innate masculinity - and be accepted thus - then he will have done them, and us, a favour. In that sense he is, whether intentionally or not, a first-class freestyle ambassador and deserves respect.
As to the undressing, my guess is that Mark simply wanted to demonstrate that he had a normal male body, albeit one that has benefitted from some grooming and toning, and that there was nothing 'unusual' (e.g. piercings, tattoos, pretty lingerie) to reveal. It was not really necessary but served to demonstate further his frankness and lack of inhibition, without being salacious in any way.