I don't belittle people with McJobs; I feel sorry for them. My own daughter worked bloody hard for a shitty supermarket chain on the minimum wage for a year before going to university and I have worked on factory floors, farms and building sites.
It's my experience that most people with McJobs don't choose them - they do them because there's no other option. They tend to be the ones without the qualifications.
And as for choosing not to take exams...well, there's a whole lifetime for 'if only's.
There aren't many things in life that I'm proud of, but one was when I took a fellow labourer along to adult literacy classes so he could learn to read. He hadn't been to school (his family were travellers) and he felt crippled by his illiteracy and too ashamed at 23 to admit it, so we both went along to the free Camden council classes together. And there he was happy to dive headlong into that free, fascist corporate education system that you decry. He did his City & Guilds and last I heard he was running his own building business and doing very nicely. And determined that his own kids would go to university.