A) It's absurd to blame the entire race because of the actions of its worst members. We're far from perfect but even with all the violence in the world today, we're at the minimum all time violence per capita. And if you accept Star Trek mythology we keep moving in that direction. After nearly wiping ourselves out, of course.
The Changelings operated as part of a greater whole--a collective, if you will, and we saw zero evidence in the show that, aside from Odo, there were any Changelings that shared Odo's sympathy and empathy for solids. (If I'm wrong, I apologize, it's actually been a bit since I've rewatched DS9).
It's not the same thing as saying that everyone of a particular race is a criminal, for instance. It's a unique situation where their entire race operates as a contiguous whole--a single Great Link. We have to basically assume that everyone is on the same page ethics-wise in this Great Link. The only reason Odo isn't (and even he gets close to being reabsorbed into their racist philosophies) is because of his separation. The Changelings have a startling philosophical uniformity that isn't seen in any other species save for the Borg, who obviously work as one hive mind 24-7 and thus are even further down that road.