1. You can fill your own car with gas, but some people can't, or prefer someone more knowledgeable to do it for them. Some people like the comfort of having someone bag their groceries for them, or have disabilities that necessitate it. Some people are old. Today you learned.
2. Your economic system is not different than theirs. Everybody NEEDS a job to support themselves, their families and to be functioning members of society. That means jobs that can easily be automated won't be automated. Also, you may make a lot more money than that kid bagging groceries to make a few bucks for himself, but at least what he does actually helps someone. What we here on Hacker News do is mostly build imaginary products that will be gone and forgotten quicker than you can say "Al Bundy".
3. Not only that, all of us here have basically written our own replacements and made ourselves obsolete. Something tells me your job isn't really needed too.