I can only speak to my personal experience. To the extent that I am uncivil (and I freely admit I am at times), it is in reaction to people (typically on the political right) who refuse to concede even an inch of comity when I acknowledge the imperfections of the world/politics/government/etc.
I'll hear, "TEH STOOPID EBIL LIBRUHLZ IZ STOOPID...AND EBIL...AND MUST BE STOPPED!"
I'll reply, "Yes, I know government officials tend to fall into corruption, which is why we need adequate oversight."
The response will be, ""TEH STOOPID EBIL LIBRUHLZ IZ STOOPID...AND EBIL...AND MUST BE STOPPED!"
I'll admit, "Yes, governing institutions are subject to 'regulatory capture' and we need to account for that."
The response will be, "TEH STOOPID EBIL LIBRUHLZ IZ STOOPID...AND EBIL...AND MUST BE STOPPED!"
I'll concede that Hilary Clinton is a flawed presidential candidate (while still expressing some preference for her over Donald Trump).
The response is almost always, ""TEH STOOPID EBIL LIBRUHLZ IZ STOOPID...AND EBIL...AND MUST BE STOPPED!"
At which point, I'm done being "civil." Right Wing Authoritarian F***tars who are more interested in ranting and demonization can go Cheney themselves, and I have no qualms using equally "uncivil" language, because I WILL NOT concede the rhetorical space to them in the name of preserving some abstract notion of "civility."