What does 上纲上线 mean?
上纲上线 means raise common things (actions, opinions) at the level of big issues about nation, society, morals or politics.

A: 好啊, 你喜欢外国货是吗? 你怎么不买国货? 叛徒!

(A: Wow. You like foreign products? Why didn't you buy products made in our country? TRAITOR!)

B: 别上纲上线, 完全没道理.

(B:stop, that's nonsense.)

A: 我觉得不一定非要让座, 我也很累啊.

B: 你真没素质.

A: 你总是喜欢上纲上线, 让不让座跟素质有什么关系?