Tranzgender does not need cizgender as an opposite in a binary. Trans believers have a gender identity at odds with their sex. Their 'opposite', in a binary, would be a person with a gender identity congruent with their sex. But most of us don't have a gender identity at all. 

Having no gender identity is NOT the opposite of an incongruent gender identity. 

The very people who deconstruct binaries they don't like are busily constructing new ones and imposing their bullshit identities on us.

Identities are a personal interest and they are chosen or socially negotiated; not something you just slap on people as a label because you need an opposite pole in a binary to make sense of your own magical thinking. 

It's selfish and colonial. 

I don't identify as being my age. 
I simply am that age. 
I don't identify as having 8 fingers and two thumbs. 
I have them. 
I don't identify as a man. 
I am one. It's not choosable, deniable, adoptable, or something to 'identify' as. It is an immutable material descriptor.

We do not need an opposite pole to everything a person might tell us they are. We're not the opposite of the bloke with a diaper fetish or who identifies as a child.

Identity politics is bad enough. But when people start to impose their waffle on the rest of us, we can fight back. 

If you do not feel 'cizgender', do not accept the label. It's a slur. Do not let them lie that this is because you are privileged, speaking from power, and have a blind spot. That's what cults do. Gaslighting your reality because it doesn't fit their narrative. It is manipulation to aggressively make you adopt their fallacious thinking. 

Fight back. We are NOT cizgender. No such thing. It's a faux political identity to show solidarity with transgenderism. If you don't accept their waffle, don't allow yourself to become politically caught up in it or subject to it.  

You are on VERY safe ground rejecting cizgender.   

If they tell you they can deconstruct sex and gender binaries, but change the rules when you deconstruct their tranzgender/cizgender identity binary, you know they are not acting consistently with their beliefs. They are manipulators, hypocrites, and not to be trusted.

You are on VERY safe ground rejecting cizgender.
It is a fake and imposed identity.