Well, you can't generalize racial attributes like that. Klingon culture nominally values honor, but we've seen our share of devious, backstabbing Klingons, from the Duras family and its supporters to the High Council that covered up that family's crimes and blamed them on Mogh for political expediency. And we've certainly seen decent Romulans now and again, such as the Unification underground members.
So maybe the current government of the Klingon Empire (under Martok) can be trusted more than the Romulan governments we've seen over the past couple of decades. But that doesn't mean the Klingons couldn't succumb to corruption again or that the rank and file of decent Romulan people couldn't kick out their corrupt leaders and put some good ones in their place.
(And there's no such thing as a "warrior race" any more than there's such a thing as a "beekeeper race." Warrior is a function within a society, but no society can exist without people serving a variety of different functions. At most, there can be a race whose dominant culture in the current epoch defines warriors as the most respected and valued members of society. But that, like the decency or corruptness of a government, is a changeable thing, not an essential racial trait.)
