Isn't the word SH++ a slang word rather than a swear word of which many are far worse & FAR more evocative ??
Indeed. It is a reminder of essential physiological processes which are somewhat distasteful and shameful. We therefore remove all reference to them in our interactions with other people. In the USA, where that joke came from, the word has had two interesting semantic consequences:
1 Removal of all references to the process in in everyday life with euphemisms such as "bath room" and "rest room" being invented. In Europe we too have a euphemism - "WC".
2 The adoption, by freewheeling, young, unconstrained individuals of the word "shit" as a kind of portmanteau, general word meaning just about anything or everything they couldn't be bothered to recall the real name of.
Our distain of talking about faeces - using any appropriate word - probably results in the unnecessary early deaths of thousands of people who ignore the early signs of colorectal cancer.
Laughing at ourselves is not the only reflective activity we should practise.