There are two threads running here - the original questioner was, I'm sure, referring to those who deliberately pretend to be of the opposite gender to their true gender - for what purpose, if there is a purpose, I can't determine.
The other thread is one in which people talk about genuinely feeling sometimes that they are 'in the wrong body' and it is with those people ! genuinely sympathise as to their confusion.
To those latter people I would say its perfectly fine to choose whatever gender to declare as theirs - but if it is different than their apparent bodily/birth gender to say so, to avoid confusion on the boards. You will find here on Zity people who will empathise with you and who will be willing to discuss your confusion with you, hopefully to help.
To those who deliberately state an opposite gender with intent to deceive I have nothing but disdain for you and for whatever reason you do this. There are a fairly large number of alleged 'females' who slip up eventually by referring to their 'cock and balls' or to their 'prostate', when of course they have neither. There are too, but fewer, those who are female but pretend to be male.
I've pretty well lost count of those who I chat to as female who go as far even as arranging or at least proposing a meeting and at the last moment almost will say 'actually, I'm male - does that make a difference?' well of course it does - I'm no liar and I won't tolerate for a moment those who are!