It's a peculiar quirk of the tech industry that "changing the world through X" is a reasonable expectation. Bus drivers don't wonder how they can make a difference through bus driving. They do their shifts and then go volunteer at the hospital, food bank, homeless shelter, etc.
Point being, you have an urge to help people. Then help people.
Now, you'll obviously add the most value to organizations that need Drupal, but free technical help is usually not "free as in beer" as much as "free as in puppies". Setting up someone with a slick technical solution almost always comes with some required maintenance fees, organizational knowledge, operational costs, etc. That is, it's hard to give away tech in a way that's sustainable. Even tech training has limited use if you're not prepared with next steps for the trainees (college applications, concrete job prospects, immediate personal benefit, etc.).
That being said, information can be given away effectively, as you learned after Katrina. Maybe some community is just missing certain information presented well. Drupal is great there. Other people are great at writing middleware for CAN buses. They probably have fewer opportunities to apply tech to help humanity than you do. They'd be better off pitching in at Habitat for Humanity, and maybe you would be too, just to start.