"Wholesome environments are not a synonym for straight," Alan Mishael told a three-judge appellate panel.
Mishael represents Vanessa Alenier, who took custody of the baby days after he was born Jan. 9, 2009. She fostered the child before requesting an adoption, which a lower court approved in January.
But the state Department of Children & Families then seized the boy from the mother, who they declared unfit because she is lesbian.
A 1977 Florida law lets gay men and lesbians foster abused and neglected children but forbids them from adopting.
Three lower-court Florida judges recently declared the law unconstitutional and approved adoptions by gay families.
"If the Legislature wanted to prohibit blind people from adopting, you would defend that too?" Court of Appeal Chief Judge Juan Ramirez Jr. asked Department of Children & Families attorney Ronald Lathan.
"The state has the right, as does the department, to articulate criteria and eligibility standards for adoption," The Miami Herald quoted Lathan as saying. "The primary concern (for such standards) is the best interest of the children."
Judge Leslie B. Rothenberg said when the law was passed there may have been "a misconception ... that homosexuals would abuse children."
"We've progressed since that time, thankfully," she said.
The court is not expected to make its decision soon.
An earlier challenged adoption by a Miami-area gay couple has been pending before the appeals court for more than a year.