Look up authoritarian parenting vs. authoritative parenting.
Oh, and you don't want your kids to think they are a 'speck of dirt'! Do you really want to send a person who thinks they are a 'speck of dirt' out into the world to get a job, find relationships and be all they they can be? What kind of jobs and relationships do 'specks of dirt' get?? You're supposed to tell them they are strong and smart and to teach them how to navigate the world in respectful ways and how to respect themselves. How does calling them a 'speck of dirt' leave them with any self-respect?
And be really, really GLAD that your kids question you and are not robots. you want them to question authority and to use critical thinking. You don't have to give them their way, but don't squash questioning and critical thinking.
This is a good teachable moment for you and your child. Scully is right. Model appropriate behavior.
(my dad did this number on me and let me tell you that at 43 years old I still have his stupid words running in my head, telling me I'm nothing. Even though I know its not true...)