There isn’t any good reason to hit your children as discipline. It may stop the behavior but it is gonna teach kids to use violence to deal with conflict with their peers or cause them anxiety later in life.
Spanking is coping for the parent, it isn’t effective or fair for the child. That being said, fear works and being generally gentle doesn’t so I understand why some parents feel like they have to. But it causes more damage than it fixes.
If you feel overwhelmed by parenting there is nothing wrong with seeking help via family therapy or even hiring a coach to assist you on how to handle difficult discipline situations with difficult children