Well, I kinda meant "why do the Galactics theorise humans developed in such a way as to make all that insanity possible". What were the...

Ah. Yes. Well… That’s the problem.

Humans are the statistical outlier, as far as Galactic civilisations are concerned. They survived a Death World long enough to colonise other planets.They continue to treat mortal threats as fun. And generally should not be allowed near simple alcohol.

The working theory is that, should a species originate on a Death World, they go mad or they go bad [usually self-immolation, but sometimes, just avoided]. But there are very few examples that ‘make it’ as far as space travel.

Some Galactics use humans to deal with the 'bad’ portion of Death World survivor species. Those examples being no dummies, would want to take over much easier planets to live on. The humans use a stunning combination of the carrot, the stick, and the slick sales campaign to convince said examples to both decamp and find somewhere even better to be.

The rest just use humans as a threat. Since we’re the only species from a Class Three Death World who can be negotiated with on friendly terms. [Class One being the tamest of Death Worlds, and Class Five being the most severe. Though Earth does have Class Five flora, fauna, mycotta and geography, it’s not the entire planet, nor the entire inhabited surface, so they just suffice to raise the overall score.] Class One and Two Death Worlders generally take one look at footage of us and immediately play nice.

No other species quite like humans has ever been found. The Galactic Alliance is secretly glad about this.