They were arguing for basic human rights in the workplace. Things like child labour were still super common and were among the practices the Luddites wanted to abolish. Along with the workhouses they wanted to replace with protection for workers (they didn’t have the word for it but they wanted a social security system).
They smashed the machines for leverage. There was little labour law at the time. Most of it was written by the capital holders with the help of the constabulary. Things like showing up to work on time or no pay, etc. Violence, controlled violence, was the tool they used to try and get the capital holders to the table and negotiate.
It failed, as we know, and it was a bloody failure. People were executed and jailed. The movement became a pejorative for someone who is backwards and against technology and progress.