He's probably OK with being called a "man," too.

Shatner's argument--as far as I can make any sense out of the Twitter mini-rant--seems to be that labels are great if you embrace them but not if they're imposed on you. That rule is workable on an individual level, but how should we speak of people collectively, given that any group contains a range of preferences and we don't know what those preferences may be at any given moment? In Shatner's view, we should choose whatever label is easily comprehended by cisgender men like himself and whatever maximizes their power over others who don't fit the label! So, for him, "man" (minus the "cisgender") is a great label as long as it serves him and people like him, and if it also forces people unlike him to conform, to be othered as "not a real man," or to be invisible and uninterpretable, that's, like, an extra benefit from his POV.