You definitely have the right to not rent to someone because they are a convicted sex offender.
You can't reject someone based on the seven protected classes that Veronica listed including a disability. You may still reject an applicant that is in a protected class for another reason such as being a sex offender. You may deny them based on the fact that that they are a convicted sex offender but you can not deny them based on the fact that they have a disability.
Fair housing aims to eliminate discrimination in any housing related activities. The belief is that every person has the right to buy, rent or obtain a mortgage without being discriminated against because of their background.
The seven protected classes are: race color religion national origin sex disability familial status
The Fair Housing Act does not prohibit the denial of housing on the basis of credit worthiness, previous rental history, or criminal record.