Whenever I'm at a restaurant and there's something wrong with the food

Sounds like you go to some shitty restaurants then

There are logical and illogical fears.
Illogical: I don't send my food back because it might feel unwanted and out of depression turn into a bat and fly off my plate
Logical fear: That is a logical fear

The only reason I might send something back is if it has something I'm allergic to that I specifically asked be excluded from the dish. I personally don't have food allergies but some family members of mine do

Some advice from somewhere: If you add salt to the meal before you send it back, you will know if it's the same dish or if they actually made you a new one. Although if it's burned, you should be able to tell if the new one is not....

I have a good friend that is a chef, and he says that he appreciates it when people are honest and send back the food because then he can learn from his mistakes and make better food in the future.

The only time I've ever sent food back was when they overcooked my steak. I was paying like $40 for a steak. You're damn right I want it cooked right.

I try not to because I don't wish to be rude. But in a situation where something is burned badly or something then I'll make an exception.