There are entire books written on the ethics and impacts of jokes. Punching up vs punching down, the implications of the social power dynamics, context, and the like.

If you as a supposed adult can't look at the world around you where trivializing the Holocaust has been a tool used to fuel the rise of fascism and extrapolate out why empathy is good and trivializing mass scale deaths is bad under the guise of fat jokes then no, I can't explain to you who is harmed and why.

Some people were born to throw cold water at anything fun.