Of course, that particular combination of laws seems very odd from this side of the Atlantic. But before I congratulate myself that it is not yet so bad with us, I should remember that I live in a country where alcohol and tobacco are legal drugs, but marijuana is illegal. In public health terms, the handgun vs. sparkler comparison may not be too far off the mark.
In both cases, the culprit is of course history, with its long train of consequences stretching far beyond the reach of foresight, which makes every human choice (no matter how obviously right at the time) effectively a pig in a poke. We're constantly playing moral Twister, trying to invent new and increasingly tortuous ways to justify our various incompatible beliefs and practices, till the whole mess falls over in a way that makes the gods (and Thomas Kuhn) chuckle.
Until that point, however, we must live with all the ridiculous and obsolete things that act as a drag on human well-being, from the House of Lords to QWERTY keyboards. Being left-handed, I've actually some affection for the latter, but then I fear that I'm rather ridiculous and obsolete myself. My comfort is, it's the human condition.
* ETA: Deaths from firearms in the United States run at around 30,000 per year. The figure for deaths from fireworks (for the one year I've been able to get hold of) was four. It's not recorded whether any of these involved sparklers, but I sincerely doubt it.