"Derailing" is used to prohibit comparisons ("you can't talk about that, it derails my narrative"), like how leftist talk about Trump and righties talked about Obama. I brought up the extreme hypocriticalness of the left in the way they talk about Trump after their constant whining about how the right talked about Obama. You don't get to claim the moral high ground wile being extreme hypocrites.
The same thing happened when we talked about the use of filibusters (ages ago). I was accused of "derailing" because I pointed out that both sides did it when they weren't in power. See, the one side wanted to demonize the other side and didn't want anyone to "derail" that narrative with facts.
On another site, people were talking about Trump giving "historically black colleges" 6 times more than Obama. Guess what the leftists did. Yep, they played the Obama card like we see here. They wanted to slag off Trump for not giving enough money to HBCs and didn't want the facts to get in the way.
"Jeffery Dahlmer is the only serial killer to target males."
"Umm, John Wayne Gacy also targeted males"
"Stop fucking derailing!!!"