Halstead has actually been one of the unit to stay closest to the straight and narrow (with some exceptions usually tied to his PTSD), talking Upton down from going too far in the latest episode and certainly never facing the kind of assumption that Burgess recently leveled at Ruzek after he killed a man.
None of the cops of Intelligence at this point have entirely avoided crossing lines (although some have definitely done worse than others), but bending the rules generally happens as they try to find justice for people who have been wronged.