So how many lives have garbagemen changed in the way OP talks about? How much impact do workers in a steel mill have? What about other simple but very common (and very necessary) jobs like the building maintenance and cleaning?
There are a lot of jobs out there that do not really directly advance society or change human lives on a large scale or have any other big impact but they still exist and people make a living off off them. And I would say most jobs are like that - (very) few people ever get the chance to actually do something truly great, meaningful and have real, direct impact on "real people".
And despite all that, what do I contribute to society although I am quite unimportant? I pay my taxes, my insurances and thereby contribute to not only my own well-being. And any software I might have written or I am maintaining is doing something useful somewhere in a very specific context and it helps people do their job which again has some impact on others and enables a company to exist and do something people are willing to spend money on and thereby that company offers jobs and etc...
Nothing wrong with being "just" a small wheel in the humongous machinery that is our world. If you ask me, it is actually (a much welcome and appreciated) luxury of modern life that we can allow space for all those "weirdos", all the diddling-around and all those strange new jobs that "real people" don't understand.
Also, it is pretty megalomaniac to assume everyone working "in IT" or reading HN is really such a rockstar and genius that they might find themselves in a position where they suddenly change the lives of thousands of people. Just because you know C or Javascript or Rails doesn't automatically make you a shining beacon of advancement of the human condition. Many people who are much, much smarter and better educated than you and me are living just as "unimportant" lives and will very likely never have a chance to become the next Einstein or Robert Koch. Learn to be more humble.
And countless scientists and artists who did change the way we think forever only did so long time after they were dead because during their lifetime, they were lucky not to get burned at the stake or starve to death in bitter poverty.