Also based on treating people fairly if you think about it. Can't treat someone like a convicted armed robber for something they perhaps done foolishly did in their teens and have stayed on the straight and narrow since.
There is an exclusion list where you still have to declare, such as working with children, law enforcement etc
Also, the formula for when a conviction is classed as discharged (and you no longer declare) is a rather complicated affair though.
USA is a strange beast when it comes to things like this. Willingly ban Kinder chocolate eggs to protect children's health but allow 'open carry' policy on Automatic weapons in some states!! However that's a whole other discussion

Back on track it may differ state to state
This is an exert from your law surrounding this
Title VII
Title VII prohibits discrimination in every aspect of employment, including screening and hiring practices. The Equal Employment Opportunity Commission (EEOC), which enforces Title VII, issued guidance in 2012 on employer use of criminal records in hiring. The EEOC has long warned that an employer’s blanket policy of refusing to hire anyone with a criminal record could be discriminatory, given the much higher arrest rates of African Americans and Latinos.
In its policy guidance, the EEOC made clear that disqualifying applicants based on criminal records could lead to two types of discrimination claims:
•If the employer treated applicants of different races or nationalities differently in the hiring process, that could lead to a “disparate treatment” claim. For example, an employer that runs criminal background checks only on non-White applicants, excuses minor offenses by White applicants while excluding Latino applicants for the same types of records, or assumes that an African American with a youthful drug offense poses a safety risk while a White applicant with a similar offense did not, that employer is treating applicants differently based on their race or national origin.
•If the employer applies a uniform policy that has a disproportionately negative effect on applicants of certain races, that could lead to a “disparate impact” claim.
Because employers could have perfectly sound reasons for wanting to exclude applicants with certain types of offenses, the EEOC has provided a three-part test employers can use to make sure that their criminal record exclusion policy screens out only those who pose an unacceptable risk. The EEOC instructs employers to consider:
•the nature and gravity of the criminal offense or conduct
•how much time has passed since the offense or sentence, and
•the nature of the job (including where it is performed, how much supervision and interaction with others the employee will have, and so on).