I do believe the MU humans became unwilling victims of their environment that somehow propelled them into Imperial brutality that we saw in the shows.
This was most aptly explained in the old DC comics, that postulated that the Imperial Federation was born out of a catastrophic loss of the Earth/Romulan war (as opposed to the win in the normal Federation universe). Earth humans and, to some extent Vulcans, were subjugated under Romulan rule for years until an underground insurgency rose up, stole a bunch of warships and destroyed the Romulan homeworld (or something to that effect). The prevailing opinion from that point forward was "NEVER AGAIN!", adopting a military doctrine of preemptive supremacy, effectively making them as bad as the Romulans once were. The rest, as they say, is future history.