Even so, forget it. You may conclude that there is nothing to prevent you from speaking your mind since you no longer have an association with the firm. You may think that since you no longer work there, the former company has no hold on you or way of doing you any harm. The fact is, when you criticize a former employer, the prospective employer does not think bad of the former employer. He or she only thinks bad of you for doing the criticizing.
Employers tend to side with employers.
It can boomerang right back on you. The prospective employer starts wondering if there is something wrong with you, or you would not have had that kind of trouble with a former employer. In addition, appearing to be a complainer turns off the prospective employer. For example, a manager made a good impression initially in an interview, but then suddenly turned negative. The employer described the areas he wanted the person who would be hired to handle.