When most people hear of secession and civil war they have an image of dumb rednecks with shotguns lead by Alex Jones. Then they say how impossible it is for citizens to fight the military which may or may not be true but the more likely scenario is of a schism within the military of highly trained, heavily armed soldiers performing a coup or going rogue against the military. So when the leftists imagine a revolt they always envision the military on THEIR side when any real civil war will have a military, political leaders, and infrastructure on both sides.
Considering that the majority of the military are all white, male, christian, conservatives who are being oppressed with leftist tolerance, the splinter faction scenario is possible. Another possibility is that the white christians simply stop joining the military and as diversity becomes the norm within the military we go the way of Rome and fill up the rank with foreigners and aliens. Similarly as Rome, once the decline accelerates the foreign born military will not hold loyalty to anyone and will turn to looting and piracy once the .gov checks stop rolling in.
But leftists don't live in reality. They long for ideals and not realism. For a society to function properly it must focus its intent on the mainstream of the culture not the outlier. The transgender is such a tiny minority that paying them any mind within the collective is wasted since their issues don't matter.