Lessons should be compulsory as they are today because education is the future of our society. Although many children would prefer not to go to school, the importance of schooling for success in the adult world is widely recognized and not giving each child a proper education will create many adults that are not equipped to function in modern society, which will result in a myriad of social problems in the future.
In deciding to move over to the common core we have come much closer to lessons being compulsory. I believe some topics should be required including topics in math, science, reading, literature, English, history, and social studies. Some school systems would only do the bare minimum and skip some topics, so it is best that essential topics be compulsory.
Some lessons you don't need for jobs eg : unless you want to be a history teacher, learning history is not usefull (but admittedly fun). For GCSE you can drop languages so because I speak german I can drop french - why learn french if I never use it? Honestly, some are useless but some (like sport are required for a healthy body)