Was Will "patently lying" when he said killing someone is the ugliest thing in the world?

I don’t think the show indicates that as such. In his follow-up with Abigail in Releves he doesn’t completely take back his statement, though he acknowledges that after he felt terrified he felt powerful. And in season 3 he says to the imaginary version of her “The wrong thing being the right thing to do was too ugly a thought”. I think he can consider something both beautiful and ugly enough he doesn’t want to go on living.

In reference to my tags here. Looking at the way Dancy plays that moment, it’s hard for me to see his line as anything other than a lie: there’s such roiling self-loathing running underneath both his voice and his skin. Will at least thinks it’s a lie – we are certainly welcome to debate whether or not Will is accurate in thinking that, but that’s a separate question – but he must tell it because he wants to protect and console Abigail, and protect his own image in her eyes. Compare with the naked honesty of “I liked killing Hobbs.”

Will sees killing as beautiful and wrong, but wrong doesn’t equal ugly. I think the allure of killing for Will is in part aesthetic, hence the visual lusciousness of the show so deeply rooted in his perspective. As for “the wrong thing being the right thing,” that deliberately confusing syntax makes me strongly doubt the veracity of this line, too. Will obfuscates the truth through riddling language. The truth is that he is obsessed with that other world in which the wrong thing turned out to be the right thing. That thought isn’t ugly to him at all, not nearly as ugly as it should be. That dream world is so compelling to him that he’s finding it hard to live in the present moment. And the person to whom he addresses that line – Abigail – is a denizen of that dream world!