It's not Little Boy that created a runaway supercritical explosive nuclear reaction, it was uranium that created a runaway supercritical explosive nuclear reaction.
Except that that uranium had to be mined, refined, separated, shaped, and placed into a gun-type fission physics package.
The toxic people you mention existed before Reddit (and Facebook, Twitter, YouTube, or other various online media). However they weren't manifesting the same effects as we're seeing now, for the most part, until Reddit (and Facebook, Twitter, YouTube, or other various online media) came along.
It's not the components that have changed, but the relationships, vectors, and mediation between them.
We could, of course, note that there were earlier periods in which we saw similar types of situations evolve. And I could respond in turn that many of those instances were themselves the result of changes in the media landscape: AOL and Usenet, 24 hour cable television news, talk radio, FM radio, CB radio, handheld megaphones, Xerox machines, mimeographs, television (both terrestrial, cable, and satellite), radio, large-scale public address systems, high-speed printing presses, widespread literacy, population concentrations in cities, railroads, and more.
And from these: the 2003 Iraq War, the Gigritch "Contract on America", the Rwanda massacre, the Yugoslav civil war, the Reagan and Thatcher revolutions, the 19760/70s Vietnam War protests, the 1950s and 1960s Civil Rights movements, McCarthyism, Father McCoughlan, Fascims and Nazism, the Russian Revolution, the Revolutions of 1840, the Chartist Movement, the French Revolution, the American Revolution.
Changing how a system receives, transmits, and processes information will fundamentally change that system itself.
The Internet is, in significant part, toxic.