Modern lead-free solder is excellent, but most hobbyists who never buy solder only have a roll of historical lead-free solder from when it was crap, have awful experience with it, and pass that experience on. You can still buy leaded solder everywhere today and the flux is not as nasty as the ancient ones. Make sure you don't mix the two as lead-free solder doesn't like to stick to leaded and vice versa. So for repairing old stuff leaded solder is still important, but it's no longer a compromise to use lead-free. Also, wash your hands after soldering!