That seems like the definition of a slippery slope, and not the fallacy. How do you ever quantify "intangible harm". If I make a YouTube video and call a bunch of people peepee poopoo heads and they actually experience genuine emotional trauma from such an abhorrent act, am I then liable for paying them hundreds of millions?

I'm not saying that emotional damage isn't very real and devastating, but it's certainly not something on which our courts should base their outcomes. It's too subjective, not provable, and very difficult to quantify.