A lot of the hate emerges from what Pettine was able to accomplish by comparison.
Pettine was able to recognize the strength of his players and play to those strengths. several under his leadership - mcKelvin, a Williams, Dareus, turned their careers around.
Hacket is not able to identify or play to the strengths of his players. Consequently, capable players run the risk of being run out of the league under Hacket.