This, of course, is the result of having an improperly drawn red-flag law, not the result of having a red-flag law per se.
Only people with close long-term knowledge of the respondent (family members, teachers, co-workers) should be able to bring complaints, and either evidence or multiple complainants testifying to the same behavior, writings or utterances that suggest the person is a danger to self or others must be presented to a judge with the respondent able to present countervailing evidence and testimony in an adversarial hearing. If the red-flag law doesn't have those features, it fails to provide due process. Massachusetts's red-flag law doesn't provide for due process, and thus is not an counter-argument to properly drawn red-flag laws which do.