Why would someone want to eat the poop tube or liver of an animal?

Let's face it, people are disgusting. 

They didn't want to. They originally had to make due with what they were given. Through the generations, tasty ways were found to prepare garbage and it became acceptable, if not a delicacy.

that's very horrible pop tube

You are maybe cooking the liver wrong.  

That's part of the deal when meat is hard to get, they use everything but the oink. And when times are good, it's tradition!

Generally, people do not eat the intestines ['poop tubes'] of animals, except as emergency food in times of famine or war. Otherwise, it is used to make pet food. Liver, on the other hand, is delicious with bacon, carrots and onions in a casserole.                                                          

When the alternative is starving to death, you adapt. 

Is that any worse than eating it's leg?

That's part of the deal when meat is hard to get, they use everything but the oink. And when times are good, it's tradition!

That's disgusting according to you and an insult to those who do. Why would people eat the flesh of another living animal, that's just cruel and gross. All that blood(myoglobin) and sinew, it's another living animal, how could you!??? Hearing that cartilage break when you are eating chicken wings is horrible. The rest of the world spends billions on developing biological weapons and the Swedes have Surstromming. I'm gonna go cook some chitterlings now.