It's when a Gryffindor and a Slytherin have much in common that the real problems start, because then they both have ambition and courage, but are often pursuing opposing ends. So no wonder Phineas Black would curse the Gryffindors for their "pointless heroics," because said heroics are standing in the way of his own ambitions.
Ah . . . not only that; the house of Gryffindor would also be more likely than Ravenclaw or Hufflepuff to uncover the plots of Slytherin, given their tendency to actively look for opportunities to test their courage. Similarly, where a Hufflepuff or Ravenclaw may pursue solving quarrels with Slytherin diplomatically by perhaps addressing a teacher, a Gryffindor would openly oppose them without hesitance—for better or worse (e.g., Harry pursuing Malfoy on a Broomstick, which turned out very lucky for him).
This Gryffindor tendency to come into conflict with injustice may be why you mistook the Hufflepuffs as not standing their ground and fighting for justice when need arises. Availability heuristic, I think (I am not too sure, it being too-late-o'clock and all).
